Rhythm and blues: the theory and treatment of seasonal affective disorder.

Seasonal affective disorder (SAD) is a depressive disorder which occurs during the winter and remits in the spring and summer. It differs from non-seasonal depression in its seasonal variation and in the presence of neurovegetative symptoms such as increased appetite and hypersomnia. This review is aimed at clinical practitioners and presents a detailed description of the syndrome before discussing the assessment of SAD and the current treatment of choice of phototherapy. Particular attention is paid to the impotant issue of differential diagnosis during assessment and the practicalities involved in the administration of light therapy during treatment.