Objective: Bright light treatment is an established treatment for Seasonal Affective Disorder, but in non-seasonal depression research results have been contrasting. Method: This study was designed as a 5-week controlled, double-blind, parallel trial in out-patients with a diagnosis (DSM-IV) of non-seasonal major depression, randomized to either active treatment (white light, 10 000 lux, 1 h daily) or placebo treatment (red light, 50 lux, 30 min daily) and concomitant treatment with sertraline in both groups. Results: One hundred and two patients were included in the study. Analyses showed that on all used scales the reduction in depression scores was larger in the bright light group than in the dim light group, and this reached statistical significance on all observer rating scales and on the SCL-90R self-assessment scale. The HAM-D₆ was the most sensitive scale to measure improvement at endpoint. Conclusion: The study results support the use of bright light as an adjunct treatment to antidepressants in non-seasonal depression.