The majority of injections intended to be intramuscular are actually delivered into fat in the area of the buttock in most of the patients having a thick gluteal fat layer. Injections of some drugs can cause tissue necrosis that ensues in scar formation and often in dystrophic calcification giving rise to ring-like densities in antero-posterior radiograhs of the pelvis. We studied the incidence and characteristics of calcifications in the buttocks frequently noted in pelvic radiographs and whether they have any realtionship with thickness and distribution pattern of the fat layer in the buttocks. Pelvic radiograms of 220 consecutive patients (110 males and 110 females) with the age ranging from 16 to 76 years (average 39) were reviewed. The area of buttock was divided arbitrarily into four quadrants by the vertical line crossing the center of the head of each femur and the horizontal line connecting the summit of each femoral head, and the upper outer quadrant was further divi ed into four quadrants(Fig. 1). We measured the thickness of the extraperitoneal fat layer at the level where it cross the iliac crest bilaterally. The results were as follows: 1. Thirty out of 220 cases (14%) showed calcifications in the buttock. 2. Calcifications in the buttock were much more frequent in female than in male (P<0.01). 3. The incidence of calcifications increased with age (P<0.01) and with increase in fat layer thickness(P<0.01). 4. Calcifications in the buttock were mostly located at the upper outer quadrant of the buttock(78%). 5. In conclusion, we assume that calcifications in the buttock are result of fat necrosis after injection into fat instead of muscle.