Purpose: The objectives of this study were designed to conduct a systematic review of clinical outcomes after osteochondral allograft transplantation in the knee and to identify patients, defects, and graft-specific prognostic factors. Methods: We searched PubMed, Medline, EMBASE, and the Cochrane Central Register of Controlled Trials. Studies that evaluated clinical outcomes in patients after osteochondral allograft transplantation for chondral defects in the knee were included. Results: There were 11 eligible studies resulting in 550 knees with a mean follow-up of 150 months (range, 30 to 261 months). The overall follow-up rate was 93%. The mean age was 31 years (range, 15 to 52 years), and 478 patients (63%) were men. With regard to etiology, the most common indications for transplantation included post-traumatic (38%), osteochondritis dissecans (31%), osteonecrosis from all causes (12%), AVN (1%) and idiopathic (9%). 63% of patients had concomitant procedures, and the mean defect size across studies was 6.3 cm2. The overall satisfaction rate was 93%. Conclusions: Osteochondral allograft transplantation for focal and diffuse chondral defects results in predictably favorable outcomes and high satisfaction rates. Patients with osteochondritis dissecans, traumatic and idiopathic etiologies have more favorable outcomes as younger patients with unipolar lesions and short symptom duration. Future studies should include comparative control groups and use established outcome instruments that will allow for pooling of data across studies. The level of Evidence: Level IV, a systematic review of Level IV studies.