Seasonal affective disorder, which is underdiagnosed in the primary care setting, is a mood disorder subtype characterized by episodic major depression that typically develops in winter when daylight hours are short. Patients with SAD experience increased morbidity and decreased quality of life. This article focuses on recognition and management of this condition. Light therapy is the preferred treatment for SAD because it is safe and easy to administer; light therapy may be combined with pharmacologic therapy. Cognitive behavioral therapy (CBT) also has a positive therapeutic effect when combined with light therapy and may help prevent SAD in subsequent seasons.