OBJECTIVE: The study investigated whether results on the Seasonal Pattern Assessment Questionnaire, which is used for diagnosis of seasonal affective disorder, differed by the season in which the questionnaire was completed. METHOD: Every third month from March 1997 to February 1998, a population-based panel of 200 men and women age 27-72 years in Gamvik, northern Norway, completed a standardized questionnaire that included all items from the Seasonal Pattern Assessment Questionnaire. RESULTS: The average score for seasonal affective disorder changed over the year. The difference between the highest score, in March, and the lowest, in September, was 8.8%. CONCLUSIONS: Results on the Seasonal Pattern Assessment Questionnaire varied by season, but did not vary by seasonal differences in the amount of daylight.