Patients with seasonal affective disorder (winter depression) from the Oslo area (at about 60 degrees N) recruited through mass media advertising were treated with 1500-lx white full-spectrum light for 2 h in the morning for 6 days. Their clinical state was assessed at baseline and 1, 3, 6, 10 and 14 weeks after commencement of treatment with an extended version of Montgomery-Asberg Depression Rating Scale (MADRS) and Clinical Global Impression. Forty patients (35 women, 5 men, age range 24 to 64 years) completed 1 week of light treatment. A subgroup of 9 patients received light in addition to ongoing drug treatment. The mean reduction in total extended MADRS score at week 1 was 48% in patients receiving only light and 56% in patients receiving light in addition to drugs. In spite of the low dose of light given, this is comparable to other reported results using light treatment for winter depression. In contrast to most other studies, however, the improvement at week 1 was maintained for the rest of the season in most patients. Only 5 patients were given another light treatment course, and another 5 were switched to drug treatment due to their unsatisfactory response to light treatment.