Stable acetabular fixation cannot be reliably achieved with the use of a hemispherical porous coated component alone in patients with a Paprosky type IIIa defect. The purpose of the present study was to determine the short-term results of a tantalum porous coated hemispherical acetabular component supported with a modular tantalum augment in Paprosky type IIIa defects. A total of 28 patients (28 hips) were treated for a type IIIa acetabular defect between 2001 and 2003 with the use of a trabecular metal acetabular component supported with a modular, superiorly placed trabecular metal augment. At an average of 3.1 years follow-up, 1 patient required rerevision for recurrent instability. The remaining hips remain radiographically stable. Clinically, the patients' modified Postel Merle d'Aubigne score improved from 6.8 preoperatively to 10.6 postoperatively. The use of a trabecular metal acetabular component with a superiorly placed trabecular metal augment demonstrates encouraging short-term results for Paprosky type IIIa acetabular defects.