Of thirty-four occurrences of bone pain in seventeen children and young adults who had type-I Gaucher disease, twenty-five were finally diagnosed as bone crises. On the basis of a bone scan with technetium-99m methylene diphosphonate, a correct diagnosis of bone crisis was made for twenty-three occurrences, with a sensitivity of 0.92. At the onset of a crisis, the bone scan typically showed decreased uptake of radionuclide at the involved site. After six weeks, a repeat bone scan of the long bones showed a ring of increased uptake surrounding an area of decreased uptake. At six months, the appearance of the bones on the radionuclide scan was normal.