A prospective study examined the attitudes, practices and physical characteristics of adults who enrolled in and adhered to a workplace fitness programme. Questionnaires on health beliefs and exercise habits were completed by 409 participants in an employee fitness programme and by 374 randomly selected non-volunteering controls. All underwent initial aerobic testing, and 20 months later 263 of the original enrollees were re-evaluated. Among the males, concern for health and belief in the health value of exercise were significantly stronger among enrollees than in controls. A higher level of perceived health and realistic expectations of the programme characterized male enrollees who went on to higher levels of exercise. For women, perceived health and belief in exercise were stronger in initial participants, but there were no clear predictors of exercise adoption. Although attitudes towards exercise generally became more positive over the programme, low-level participants came to view exercise as less "fun" and more "discipline". People who are ready for change and believe in exercise may enter a fitness programme, but adherence is influenced by personal factors such as the perceived state of health and the acceptability of the specific exercise programme.