The purpose of this paper is to describe the factors that affect compliance in adolescents with a chronic illness and to compare compliance and factors connected to compliance between adolescents with asthma, epilepsy, rheumatoid arthritis (JRA) and insulin dependent diabetes mellitus (IDDM). The data were collected by questionnaire. Altogether 1200 individuals were selected from the Finnish Social Insurance Institution's register. The response percentage was 88 (n = 1061). One-fifth (23%) of adolescents with chronic disease felt that they had complied fully with health regimens, while 60% placed themselves in the category of satisfactory compliance and the remaining 17% reported poor compliance. In each patient group compliance was promoted by good motivation, a strong sense of normality, a positive attitude towards the disease and treatment, energy and will-power, experience of results, support from the parents, nurses and physicians, and a feeling that the disease was not a threat to social well-being.