Harris and Dawson report the results of a 1-year prospective study of seasonal mood change among 250 healthy nondepressed women participating in a study of Vitamin D supplementation. All study participants were taking calcium supplement, but they were randomized to take Vitamin D 400 IU per day or placebo. Each participant completed the profile of mood States (POMS) questionnaire at four study visits. There were significant changes over the year in POMS subscale scores for Tension-Anxiety, Depression Dejection, Anger-Hostility, Fatigue Inertia, and Confusion-Bewilderment. These scores were all highest during the spring or summer. Supplementation with vitamin D did not appear to affect levels or Changes in mood scores.