The diagnosis of Crohn's disease with extensive involvement of small intestine and colon was first made in a 12 3/4-year-old girl, now 15 1/2 years old. Despite continued treatment with prednisolone and salazosulfapyridine, as well as azathioprine and metronidazole, no lasting remission was obtained. Widespread severe osteoporosis with vertebral fractures made it necessary to discontinue the prednisolone, despite endoscopically and biochemically confirmed signs of activity of the disease. Administration of cyclosporin A in this situation produced phases of improved clinical and biochemical parameters. Regular control of biochemical levels failed to reveal any drug-specific acute side-effects. Because of the increased incidence of malignant lymphoma under cyclosporin A this drug should be held in reserve in the treatment of Crohn's disease, until results from controlled studies have become available.