Background. The validity of the concept of seasonal affective disorder and the causal link to lack of daylight in winter is controversial. There is a need for investigations in large samples of the general population at different latitudes and within general research contexts to avoid selective response bias and sensitization of the population.

Methods. During a study of health effects of the air pollution from Russia in a small community at 70° north, a self-administered questionnaire was filled in by 3736 inhabitants, 60·8% of the total population between 18 and 69 years. Three questions concerned depression, sleeping problems and other problems related to the two contrasting seasons with regard to daylight.

Results. Twenty-seven per cent reported to have some kind of problem in the dark period. Most frequently reported were sleeping problems during winter, in 19·9% of women and 11·2% of men. Self-reported depression in winter was found in 11·1% of women and 4·8%% of men. Sleeping problems increased with age, while depression was most often reported by middle-aged people. The only other reported problem in winter was fatigue. The adjusted relative risk (RR) for winter depression in women compared to men was 2·5 (95% confidence interval: 1·9–3·2). Very few had problems in summer.

Conclusions. In the high north, one-third of the women and one-fifth of the men experience problems with sleep, mood or energy related to season. The prevalence of self-reported depression was surprisingly low in winter considering the lack of daylight.