Severely comminuted intra-articular calcaneal fractures often culminate in subtalar arthrosis and stiffness even after operative reduction. In some instances, subtalar arthrodesis is necessary to reduce the symptoms. Primary subtalar arthrodesis for these fractures has gained acceptance in recent years. However, few definite predictors of functional outcome after primary fusion have been found. A series of 17 patients with highly comminuted fractures were studied to determine which radiographic parameters were predictive of functional outcome. The American Orthopaedic Foot and Ankle Society Ankle-Hindfoot scale score was obtained at an average of 34 (range 12 to 157) months after arthrodesis. Radiographic measurements included the talocalcaneal, calcaneal inclination, talo-first metatarsal, and Böhler's angles, and the height of the tibial plafond, width of the calcaneus, and the presence of a medial step-off on the injured and uninjured foot. The mean Ankle-Hindfoot scale score was 78 (range 56 to 92), and the mean visual analog score was 1.9 (0 to 4). Statistically significant associations were noted between greater postoperative function and increasing age (p = .028), the quality of restoration of Böhler's angle (p = .038), and the talocalcaneal angle (p = .049). No patient had nonunion. The results of the present study suggest that the outcomes after primary arthrodesis of the subtalar joint are favorable, in particular, when the radiographic relationships of the hindfoot have been restored.