Seasonal affective disorder (SAD) has been successfully treated with bright light, and morning exposure has been deemed more effective than exposure at other times. Evening treatment may offer a practical advantage, but the optimal duration of exposure has not been established. Six SAD patients were treated at home for 1 week with 2500 lux of light given either from 6 p.m. to 8 p.m. or from 6 p.m. to 10 p.m. using a counterbalanced crossover design with a minimal withdrawal period of 1 week between conditions. Both treatments were effective in reversing SAD symptoms, but neither treatment was superior. These results suggest that evening phototherapy for as little as 2 hours may be a useful and reasonable alternative for the treatment of SAD.