A 14-year-old boy experienced multiple hospitalizations because of symptoms due to Crohn's disease involving the stomach, duodenum, and ileum. He maintained that oral corticosteroids were not effective for control of his symptoms. However, i.v. corticosteroids always relieved his symptoms. To resolve the question of noncompliance versus altered corticosteroid absorption or metabolism, our patient underwent an oral prednisone absorption study. Prednisolone, the active metabolite of prednisone, was measured in his plasma using a high-pressure liquid chromatography technique. The results led to the discovery of an elaborate deception by the patient and his subsequent need for psychotherapy. This report documents the importance of measuring plasma prednisolone concentrations to diagnose noncompliance, especially in adolescents who are overly concerned about their body image.