A ll-year-old boy with 3 months history of back pain was found to have a parathyroid chief cell hyperplasis at operation. Initial roentgenograms showed dense metaphyseal lines in the knee and wrist and compression fractures involving the lumbar spine. Two months later extensive generalized osteitis fibrosa cystica developed throughout the entire skeleton inclu-ding the skull. Serum chemistry and parahyroid hormon assay were compared before and after operation. Primary hyperparathyroidism was not corrected even after the operation and the patient succu-mbed 1 year and 6 months after the initial diagnosis.