Winter depressive episodes in patients with seasonal affective disorder are induced by light deficiency and are successfully treated by enhancing environmental light. The authors investigated the role of abnormal visual information processing in the genesis of seasonal affective disorder symptoms by examining two patients with impaired vision and recurrent winter depressions. The first patient developed winter depressions after developing a traumatic cataract in one eye, and was helped by light therapy. The second patient, fully blind since she was 1 year old, nonetheless suffered as an adult from winter depressions, which responded to bright--but not to dim--light treatment. The authors discuss the implications of these findings.