Objective: To estimate the projected population of US adults aged 18 years or older with lifetime experience of doctor-diagnosed depressive disorder from 2005-2050. Methods: Based on nationally representative survey data from the year 2006 Behavioral Risk Factor Surveillance Survey (BRFSS), prevalence estimates of doctor-diagnosed depression (minor or major, and dysthymia) were weighted to incorporate the complex sampling design and increase generalizability of the findings. The weighted prevalence data by age and sex in 2006 were then used to estimate the projected adult population with lifetime experience of depressive disorder based on the sex-specific US Census national population projections from year 2005-2050. Results: In year 2006 the (weighted) prevalence of lifetime experience of depressive disorder was 15.7% among 188,292 respondents aged 18 years or older. Female prevalence was 20.6%, which was about twice as high as the prevalence among males (11%). From year 2005-2050, the total number of US adults with depressive disorder will increase from 33.9 million to 45.8 million, a 35% increase. The increase is projected to be greater in the elderly population aged ≥65 years (3.8-8.2, a 117% increase) than in the young population aged <65 years (30.1-37.7, a 25% increase). Conclusions: By year 2050, approximately 46 million US adults aged 18 years or older will be diagnosed with a depressive disorder. The increase will be more pronounced in adults aged 65 or older. Prevention, detection, and treatment of depressive disorders might attenuate the magnitude of this estimate. Copyright © 2008 John Wiley & Sons, Ltd.