A 1-year prospective study of seasonal mood changes was conducted in 250 female Boston area residents, aged 43 to 72, who were participants in a study of vitamin D supplementation. Each woman completed the Profile of Mood States questionnaire at four study visits. There were significant changes over the year in scores for Tension-Anxiety, Depression-Dejection, Anger-Hostility, Fatigue-Inertia, and Confusion-Bewilderment. These scores were all highest or "worst" in the fall and lowest in the spring or summer. Worse mood scores were associated with fewer hours of sleep. Serum thyroxine was positively associated with higher Depression-Dejection scores in August through November and with higher (better) Vigor-Activity scores in February through May. Supplementation with 400 IU of vitamin D did not appear to affect levels or changes in mood scores.