Thirty-five patients with 41 calcaneus fractures, seen at Cook County Hospital over a 3½-year period, underwent an open reduction and internal fixation of their fractures through a sinus tarsi incision. Bohler's angle averaged 6° preoperatively and 26° postoperatively. An additional measurement, the critical angle, was defined. This angle is a measurement of the congruency of the posterior facet. It facilitated the selection of patients for an open reduction as well as allowed a determination of the adequacy of restoration of the joint surfaces postoperatively. In this series the critical angle averaged 26° preoperatively and 1° postoperatively. Followup was possible in 73% of the patients. Almost all of the patients exhibited some degree of limitation of motion of the subtalar joint, but the reduction of the fracture fragments was maintained in all cases and secondary deformity and complaints did not develop.