Introduction: The world's population is getting older, and the challenges of old age have come to the attention of healthcare systems in many countries. Depression is one of the major syndromes of old age. Given the contradictory findings regarding the prevalence of depression among older adults, the goal of the present study was to examine the prevalence and related factors of depression among community-dwelling older adults in Tehran in 2019. Methods: This was a descriptive cross-sectional study. The sample included a total of 847 community-dwelling older adults, aged 60 years or over, living in Tehran, who were selected using a multistage cluster sampling method. The data was collected by trained interviewers, using the Beck Depression Inventory-II (BDI-II). Results: 68.9% of the older adults had depression, of which 28.6% had mild depression, 33.2% had moderate depression, and 7.2% had severe depression. Being older, experiencing more stressful life events, having improper financial status, and lower education were identified as related factors for depression in older adults (P<.01). Conclusion: According to the results, a large number of older adults living in Tehran have depression. In addition, being older, having higher number of stressful life events, poor financial condition, and lower education were identified as related factors for depression in older adults. Further studies are needed to investigate the related factors for depression in the elderly.