This study examined the validity of Geriatric Depression Scale--5 (GDS-5) scores among older sedentary adults based on its structural properties and relationship with external criteria. Participants from two samples (Ns = 185 and 93; M ages = 66 and 67 years) completed baseline assessments as part of randomized controlled exercise trials. Confirmatory factor analysis supported a single-factor model for the GDS-5, the GDS-5 exhibited adequate sensitivity and specificity for screening depression, and scores from the 30- and 5-item GDS were strongly related. GDS-5 scores were strongly related with happiness and morale and moderately related with satisfaction with life, loneliness, optimism, pessimism, perceived stress, negative health symptoms, and self-esteem. As expected, GDS-5 scores were weakly related with self-efficacy, cardiorespiratory fitness, and functional fitness. Support is provided for the validity of GDS-5 scores as a measure of depression among older sedentary adults participating in exercise studies. (Contains 1 table.)