PURPOSE: To evaluate the correlation of the safe zone of percutaneous iliosacral screw fixation with sacral dysmorphism and sacral alar slope variation. MATERIALS AND METHODS: We studied the plain radiographs and the pelvic bone CT images of 52 patients. We reviewed each cases in terms of Routt 's dysmorphism and sacral alar slope variation(anterior, coplanar and posterior to inter-ICD line). We divided each cases into narrow and wide groups by the width of safe zone for the transverse 6.5mm cannulated cancellous screw. The data were analysed by McNemar x2-test and Cochran Q-test(p<0.05). RESULTS: Typical sacral dysmorphism was found in five cases(9%). Four cases with dysmorphism(80%) and eighteen non-dysmorphic cases(38.2%) revealed narrow safe zones. The sacral slopes were anterior in 16 cases, coplanar in 25 cases, and posterior in 11 cases. The safe zone was significantly narrow in the group with anterior slope variation. CONCLUSION: We could not found definite correlation between sacral dysmorphism and a narrow safe zone because the incidence of dysmorphism was too low in our study which differed from Routt 's report. An anterior sacral alar slope on CT can be a significant risk indicator for potential narrow safe zone and the risk of screw malposition.