The study assessed the spontaneous repair of large critical full-thickness defects (FTD) in not mature and still growing sheep model and compared repaired tissue after Pridie's technique to the same technique combined with type I collagen matrix. Thirty-six FTD were divided into group 1 (untreated), group 2 (treated according to Pridie's technique with 10.2 as value ratio of marrow stimulation), and group 3 (treated using Pridie's marrow stimulation technique, and covered by a type I collagen matrix) . The histological exam at 12 months showed fibrous repair of the untreated defects. In group 2 the reparative tissue showed a prevalence of fibrocartilaginous tissue. The mean ICRS visual assessment scale score was 8.9. In group 3 the reparative tissue was similar to the normal surrounding cartilage. The mean ICRS visual assessment scale score was 14.7. Subchondral drilling with defined ratio between the stimulated marrow area and the lesion area could improve the quality of FTD repair in articular cartilage in not mature and still growing stifle sheep model if combined with type I collagen matrix.