The study addresses the characteristics potentially predictive of non-response to a health survey among 2500 24-year-old males, on whom a notable amount of other data was available. The overall non-response rate was 40%, part of which was due to the unreachability of some subjects: 4% of the questionnaires were returned because of unknown addresses. Some (n = 39) of the respondents had concealed the identification number in the questionnaire, which made it impossible to link these data to those collected before in their cases. We were therefore able to use effectively the data on 1450 (58%) responding subjects in this paper. Failure to respond was more common among the subjects who had lived in towns in their youth, had not grown up in a complete family, whose socioeconomic status of the family was unknown, and whose mother was young and had a low educational level. Poorer-than-average school performance at elementary school was also predictive of a high non-response rate. Non-response was heavily associated with previous non-response to a health inquiry. Some aspects of health and behaviour in adolescense, such as smoking at the age of 14, were related to non-response to this survey, too. The non-response was higher than average among those subjects who had suffered from mental disorders (serious mental disorders, less serious mental disorders such as neurotic disorders, adjustment reactions, and psychosomatic disorders and mental retardation). The young men who were employed, were students or were doing military service at the age 24 responded better than those who were unemployed or at disability pension.