Depression generally begins before Type II diabetes and coronary artery disease; however, no data are available on whether asthma or major depressive disorder (MDD) have an earlier onset. The age at onset of asthma and depression were collected from 85 adult asthma patients with current MDD. The mean ages at onset of asthma and MDD were 21.0 years and 28.8 years, respectively. Asthma preceded MDD in 62% of cases; MDD preceded asthma onset in 24% of cases; and asthma and MDD had a concurrent onset in 14% of the cases. In asthma patients, unlike patients with Type II diabetes and coronary artery disease, depression appears generally to occur after the onset of asthma.