BACKGROUND: The Dietary Approaches to Stop Hypertension (DASH) diet is designed to lower blood pressure and improve cardiovascular health by reducing sodium and unhealthy fats while increasing nutrients, including potassium, calcium, magnesium, and fibre. While evidence supports its benefits for managing cardiovascular risk factors, gaps remain in understanding its long-term impact on preventing cardiovascular disease (CVD), particularly in terms of hard clinical outcomes such as myocardial infarction and stroke. OBJECTIVES: To assess the effects of the DASH diet for the primary and secondary prevention of cardiovascular diseases. SEARCH METHODS: We used standard extensive Cochrane search methods. The latest search date was in May 2024. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing a DASH diet intervention to no intervention (including usual care), minimal intervention, or other dietary interventions. In the context of this review, 'minimal intervention' includes brief dietary advice or informational leaflets provided during a medical consultation, without a structured dietary intervention. 'Other dietary interventions' include any other dietary programme besides the DASH diet. Participants were adults with or without CVD. The minimum duration of eligible interventions was eight weeks and the minimum follow-up was three months. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. Primary outcomes were myocardial infarction, heart failure, and stroke. Secondary outcomes were the need for coronary revascularisation, carotid revascularisation, peripheral revascularisation, all-cause mortality, cardiovascular mortality, changes in blood pressure, blood lipids, the occurrence of type 2 diabetes, health-related quality of life, and adverse effects. We used GRADE to assess the certainty of evidence for each outcome. MAIN RESULTS: Five RCTs involving 1397 participants met our inclusion criteria and were included in this review. All five trials contributed at least one intervention arm to one or more of the three prespecified comparisons. In total, 1075 participants across eligible arms were included in the meta-analyses. The difference reflects trial arms that did not meet our prespecified intervention and comparison definitions, and were therefore not analysed, though all participants were randomised within eligible trials and are accounted for in the review total. The trials assessed the DASH diet in a primary prevention setting; none evaluated its effects in secondary prevention. Participants were generally healthy adults aged 18 years or older, without diagnosed cardiovascular disease. The intervention duration ranged from 16 weeks to 12 months, with follow-up periods between 16 weeks and 18 months (medium- and long-term). The trials were conducted in the USA and Poland, with funding from public institutions, including the National Institutes of Health, the National Heart, Lung, and Blood Institute, and the Institute of Cardiology in Poland. DASH diet versus no intervention (including usual care) Myocardial infarction: one trial (144 participants) reported no myocardial infarctions in either group over a one-year follow-up. The GRADE certainty rating was low due to the high risk of performance bias and imprecision. Stroke: one trial (144 participants) reported no strokes in either group over the same follow-up period. The GRADE rating was low for similar reasons. All-cause mortality: one trial (90 participants) reported no deaths over a six-month follow-up. The GRADE rating was very low due to unclear risk of selection bias, high risk of performance bias, and imprecision. No data were available for heart failure or revascularisation needs (coronary, carotid, or peripheral) in this comparison. DASH diet versus minimal intervention Myocardial infarction: two trials (902 participants in total; 629 participants were in trial arms eligible for this comparison, based on our prespecified intervention and comparison definitions) reported limited events, with no clear differences between groups over one year (risk ratio (RR) 2.99, 95% confidence interval (CI) 0.12 to 73.04). The GRADE rating was low due to high risk of performance bias and imprecision. Stroke: two trials (reporting on the same 629 participants) reported no strokes in either group over follow-up periods ranging from six months to one year. The GRADE rating was low due to similar concerns. No data were available for heart failure, revascularisation needs (coronary, carotid, or peripheral), or all-cause mortality in this comparison. DASH diet versus another dietary intervention All-cause mortality: one trial (261 participants) reported no clear difference between the groups over one year (RR 2.98, 95% CI 0.12 to 72.42). The GRADE rating was very low due to multiple risks of bias and imprecision. No data were available for myocardial infarction, stroke, heart failure, or revascularisation needs in this comparison. AUTHORS' CONCLUSIONS: The effect of the DASH diet on major cardiovascular outcomes - including myocardial infarction, stroke, cardiovascular mortality, and all-cause mortality - remains inconclusive due to a lack of robust long-term evidence. Additionally, no trials have assessed its impact on heart failure or the need for revascularisation procedures, such as coronary, carotid, or peripheral interventions. While the DASH diet may reduce blood pressure, total cholesterol, and triglyceride levels while increasing high-density lipoprotein (HDL) cholesterol compared to no intervention or usual care, it appears to have little to no effect on low-density lipoprotein (LDL) cholesterol. Evidence comparing the DASH diet to a minimal intervention or alternative dietary approaches remains limited. Although the DASH diet has minimal reported adverse effects, the absence of long-term safety data prevents definitive conclusions on its use in individuals with or without cardiovascular disease. The certainty of evidence is low to very low, primarily due to design limitations such as high risk of bias, small sample sizes, and short follow-up periods in the included trials. Most studies focused on cardiovascular risk factors rather than long-term clinical outcomes, and all eligible trials assessed primary prevention, with no data on secondary prevention. Given these uncertainties, well-designed, long-term randomised controlled trials are needed to evaluate the DASH diet's impact on major cardiovascular events, its effectiveness in secondary prevention, and its long-term safety.