Increasing pain in the region of the lumbar vertebrae occurred in a 23-year-old woman known for the past 6 1/2 years to have Crohn's disease affecting the ileocolon. Radiology revealed marked osteopenia with collapse and deformation of the vertebral bodies. The only pointer to a bone disease was a markedly lowered serum level of 25-OH-vitamin D (less than 10 ng/ml). Biopsy from the ileal crest revealed pure osteoporosis without osteomalacia. Decisive pathogenetic factors were, in the main, glucocorticoid medication, malnutrition and the long duration of Crohn's disease. During treatment with monofluorophosphate, 152 g daily, in fixed combination with 600 mg calcium as well as calcitonin (initially 100 I.U. daily subcutaneously for two weeks, then 100 I.U. every other day s.c.) and vitamin D (3 x 1,000 I.U. daily by mouth) she became free of symptoms, and she has remained so for 9 months.