Purpose. Prostate enlargement (PE) is an increase in prostate volume in morphology. PE was also observed in some patients aged <40 with chronic prostatitis. This study aimed to explore the associated factors for PE in Chinese adult men aged <40. Methods. The medical records of 1851 consecutive Chinese adult men aged <40 in a single center were retrospectively analyzed. The checkup indicator characteristics between the PE and non-PE groups were compared by univariate analysis, and the associated factors were analyzed by multivariate analysis. Results. The overall prevalence of PE (defined as prostate volume ≥ 20 ml) in adult men aged < 40 was 10.4%. Age and the proportions of subjects with prostate calcification or hypertension were different between the PE and non-PE groups ( P < 0.05 ). Multivariate logistic analysis showed that prostate calcification (odds ratio [OR], 1.831; 95% confidence interval [CI], 1.281–2.619; P = 0.001 ), hypertension (OR, 1.528; 95% CI, 1.125–2.076; P = 0.007 ), and age (OR, 1.117; 95% CI, 1.078–1.159; P < 0.001 ) were associated factors for PE in adult men aged <40. Conclusions. The prevalence of PE in Chinese adult check-up men aged <40 was not rare. In addition to age, prostate calcification and hypertension were associated factors for PE in Chinese adult men aged <40.