PURPOSE: In the past few years, there has been a notable rise in the incidence and prevalence of idiopathic pulmonary fibrosis (IPF) on a global scale. A considerable body of research has highlighted the 'obesity paradox,' suggesting that a higher body mass index (BMI) can confer a protective effect against numerous chronic diseases. However, the relationship between BMI and the risk of mortality in IPF patients remains underexplored in the existing literature. We aim to shed light on this relationship and potentially offer novel insights into prevention strategies for IPF. METHODS: We conducted a systematic search of the PubMed, Embase, and Web of Science databases to collect all published studies examining the correlation between Body Mass Index (BMI) and the mortality risk in patients with IPF, up until February 14, 2023. For the synthesis of the findings, we employed random-effects models. The statistical significance of the association between BMI and the mortality risk in IPF patients was evaluated using the hazard ratio (HR), with the 95% Confidence Interval (CI) serving as the metric for effect size. RESULTS: A total of 14 data sets involving 2080 patients with IPF were included in the meta-analysis. The combined results of the random-effects models were suggestive of a significant association between lower BMI and a higher risk of death (HR = 0.94, 95% CI = 0.91-0.97, P < 0.001). For baseline BMI, the risk of death from IPF decreased by 6% for each unit increase. The results of the subgroup analysis suggest that geographic location (Asian subgroup: HR = 0.95, 95%CI = 0.93-0.98, P = 0.001; Western subgroup: HR = 0.91, 95%CI = 0.84-0.98, P = 0.014), study type (RCS subgroup: HR = 0.95, 95%CI = 0.92-0.98, P = 0.004; PCS subgroup: HR = 0.89, 95%CI = 0.84-0.94, P < 0.001), and sample size (< 100 groups: HR = 0.93, 95%CI = 0.87-1.01, P = 0.079; >100 groups: HR = 0.94, 95%CI = 0.91-0.97, P < 0.001 ) were not significant influences on heterogeneity. Of the included literature, those with confounding factors corrected and high NOS scores reduced heterogeneity (HR = 0.93, 95%CI = 0.90-0.96, P < 0.001). Sensitivity analyses showed that the combined results were stable and not significantly altered by individual studies (HR = 0.93 to 0.95, 95% CI = 0.90-0.96 to 0.92-0.98). Egger's test suggested no significant publication bias in the included studies (P = 0.159). CONCLUSIONS: Higher BMI (BMI ≥ 25 kg/m2) is negatively correlated to some extent with the risk of death in IPF patients, and BMI may become a clinical indicator for determining the prognosis of IPF patients.