Context: Serum concentrations of gonadal hormones have been associated with various measures of wellbeing, but it is unclear whether their association with mood is confounded by concurrent physical morbidity.Objective: To determine whether the association between serum testosterone concentration and mood in older men is independent of physical comorbidity.Design: Cross-sectional study.Setting: Community of Perth, Western Australia.Participants: A community sample of men aged 71 to 89 years.Main Outcome Measures: We used the 15-item Geriatric Depression Scale ( GDS-15) to assess depressed mood. Clinically significant depression was defined a priori as a GDS-15 score of 7 or greater. Physical health was assessed using the weighted Charlson index and the Physical Component Summary score of the 36-Item Short Form Health Survey.Results: Of 3987 men included in the study, 203 ( 5.1%; 95% confidence interval [CI], 4.4%-5.8%) had depression. Participants with depression had significantly lower total and free testosterone concentrations than nondepressed men ( P <. 001 for both). However, they were also more likely to smoke and to have low educational attainment, a body mass index categorized as obese, a Mini-Mental State Examination score less than 24, a history of antidepressant drug treatment, and greater concurrent physical morbidity. After adjusting for these factors and for age, men with depression were 1.55 ( 95% CI, 0.91-2.63) and 2.71 ( 95% CI, 1.49-4.93) times more likely to have total and free testosterone concentrations, respectively, in the lowest quintile.Conclusions: A free testosterone concentration in the lowest quintile is associated with a higher prevalence of depression, and this association cannot be adequately explained by physical comorbidity. A randomized controlled trial is required to determine whether the link between low free testosterone level and depression is causal because older men with depression may benefit from systematic screening of free testosterone concentration and testosterone supplementation.