This study was undertaken with the aim of improving the understanding of the phenomenon of compliance in adolescents presenting with chronic diseases. In 192 subjects aged 12 to 20 years presenting with diabetes, asthma, cystic fibrosis, systemic lupus erythematosus or juvenile rheumatoid arthritis, appointment keeping, compliance with prescribed medical regimens or general instructions and the filling up of a calendar describing the daily levels of fatigue were studied. Correlations (Pearson) between these various types of measurements were weak: from 0.04 to 0.26. Appointment keeping was about 90%. Overall compliance either with treatments or with general instructions was 50% only (without clearcut changes according to diseases); however only 11% of subjects presented with a good compliance with all the treatment components. Various factors (familial environment, perception of the disease and of the patient-physician relationships) were significantly associated with compliance (p less than 0.005). These results emphasize the necessity of taking care of all aspects of compliance, which is difficult to predict at this age, due to the multiple factors involved.