BACKGROUND: Malnutrition may be an important geriatric condition in adults with heart failure with preserved ejection fraction (HFpEF), but studies on its prevalence and associated clinical outcomes are limited. The aim of this study was to determine if malnutrition is associated with short-term morbidity and mortality in ambulatory patients with HFpEF. METHODS: We examined 231 patients with a clinical diagnosis of HFpEF seen at two dedicated academic HFpEF programs (Weill Cornell Medicine and Michigan Medicine) from June 2018 to April 2022. Malnutrition was defined by Mini-Nutritional Assessment Short Form (MNA-SF) scores ≤11. The primary endpoint was a 6-month composite of all-cause mortality and all-cause hospitalization. A Cox proportional-hazard models was used to examine the association between malnutrition and the primary endpoint, adjusting for race, prior hospitalization history, and the validated Meta-Analysis Global Group in Chronic (MAGGIC) heart failure prognostic risk score. RESULTS: The median age of the cohort was 73 years (interquartile range 64-81). The most common comorbid conditions included hypertension (prevalence 81%), atrial fibrillation (43%), and obesity (63%). The prevalence of malnutrition was 42% (n = 97), and MNA-SF scores did not significantly correlate with body mass index (R = -0.02, p = 0.71). At the 6-month follow-up, 62 patients (26.8%) were hospitalized and four patients died (1.7%). In a fully-adjusted analysis, malnutrition was independently associated with the composite outcome of all-cause mortality and all-cause hospitalization (HR 1.94 [95% CI: 1.17-3.20], p = 0.01). CONCLUSION: Despite a high prevalence of obesity, two out of five ambulatory adults with HFpEF are malnourished. Malnutrition was independently associated with adverse outcomes at 6 months. Future work is necessary to develop interventions that can address malnutrition.