STUDY DESIGN:: A retrospective case series. OBJECTIVE:: The purpose of this study was to describe a unique group of intercollegiate athletes who are skeletally mature and who developed symptomatic acute lumbar spondylolysis and to study long-term return to play outcome of nonoperative and surgical repair of L3 and L4 spondylolysis in skeletally mature athletes. BACKGROUND:: Traditionally, symptomatic acute lumbar spondylolysis is a defect found in skeletally immature athletes, most commonly in the pars interarticularis of L5, less commonly in the L3/L4 region, and even less commonly in skeletally mature athletes as described in this group. METHODS:: Eight intercollegiate athletes (2 women and 6 men, ages ranging from 19 to 21 y) with acute lumbar spondylolysis were diagnosed by means of computed tomography (CT) and single photon emission-CT bone scan. L3 lesions were present in 5 patients, and L4 lesions were present in 3 patients. All patients were treated initially nonoperatively with a protocol of bracing and activity modification. The healing progress was assessed through repeat CT scan. Patients who failed to respond to nonoperative procedures underwent direct repair of their pars defect through variable angle pedicle screw and sublaminar hook. Outcomes were measured by completion of the Oswestry Low Back Pain Disability Questionnaire (mean follow-up 6.5 y) and return to athletic participation. RESULTS:: All patients successfully returned to full athletic competition. Two patients showed radiographic healing and resolution of pain following 3 months of nonoperative treatment. Five patients required surgical repair of the pars defect. All of these patients eventually returned to unrestricted participation in athletics. CONCLUSIONS:: This study shows that this subgroup will generally respond well to surgical correction of the pars defect and return to uninhibited competition following conservative treatment and/or surgical repair. © 2012 by Lippincott Williams & Wilkins.