Beck's Depression Inventory was administered in a study of all students aged 16-17 years in the first year of high school in a Swedish town, and was completed by 93% of them (n = 2270). Cronbach's reliability coefficient alpha was 0.89, and there were strong correlations between item scores and total scores. A diagnostic interview focused on depressive diagnosis during the last year was conducted with 88% (n = 199) of all students with high scores (> or = 16), and with the same number of controls with low scores. A depressive diagnosis was confirmed in 73% of high scorers and 13% of low scorers. The questionnaire performed better with girls than with boys. The mean score was significantly higher for girls, and the proposed limit for moderate depression (a score of 16) was reached by 14.2% of girls and 4.8% of boys. All symptoms were significantly more frequent and more severe in girls. It was found that 20% of girls and 6% of boys reported suicidal ideation. In a factor analysis the strongest factor that emerged differed between the sexes. For boys it included sadness, crying and suicidal ideation, and for girls it included failure, guilt, self-dislike and feeling unattractive, combined with suicidal ideation. The gender differences are discussed.