In the Western world, huge amounts of money are being spent on dietary supplements, although this usage may be useless and possibly harmful. Factors that influence supplement consumption have not been well defined. This paper aims to describe relations between supplement usage and various sociodemographic and psychosocial factors. The study cohort consisted of 6,545 men and women, aged 45–65 years, who during 1991 and 1992 participated in the Malmö Diet and Cancer Study, a large-scale prospective cohort study. Data on supplement consumption were recorded during 7 consecutive days. Each participant also completed a questionnaire, covering education, work history, alcohol, smoking, perceived health and psychosocial factors such as social network, social support, job strain, etc. Total body fat was also measured. The prevalence of supplement consumption was 43% among women and 29% among men. The most important sododemographic factors were education, ethnicity and age. Female users tended to be slim, have worse perceived health and to drink more alcohol than other women, none of which applied to male users. No differences in smoking habits between users and non-users were noted. None of the psychosodal factors appeared to influence supplement consumption. Those who used vitamins and/or minerals only were more similar to non-users than those who used all kinds of dietary supplements. There was a substantial variation in consumption prevalence with season. The prevalence of supplement consumption is influenced by a number of demographic factors and also by season. To claim that supplement users are health-conscious is an over-simplification. The psychosocial factors behind supplement usage call for further analyses.