Background: Arthroscopic debridement and microfracture are considered the primary surgical treatment for capitellar osteochondritis dissecans (OCD). Healing of the subchondral bone plays an essential role in cartilage repair, while lack of healing is related to the development of osteoarthritis. To date, it is unknown to what extent healing of the subchondral bone occurs after this technique in the elbow. Purpose: To analyze defect size changes and subchondral bone healing with computed tomography (CT) after arthroscopic debridement and microfracture for advanced capitellar OCD. Study Design: Case series; Level of evidence, 4. Methods: Between 2009 and 2016, 67 patients underwent arthroscopic debridement and microfracture for advanced capitellar OCD. Fifty-four patients (81% follow-up rate) with CT scans were included (mean ± SD: preoperative, 4.0 ± 1.7 months; postoperative, 29 ± 9.0 months). OCD defect size was assessed by measuring the largest diameter in 3 directions: medial-lateral direction (coronal plane) and anterior-posterior direction and depth (both in sagittal plane). Healing of the OCD was divided into 3 categories: good—complete osseous union or ossification; fair—incomplete osseous union or ossification but improved; poor—no changes between pre- and postoperative scans. Postoperative clinical outcome was assessed with the Oxford Elbow Score (OES) at the same time as the postoperative CT scan. Results: There were 30 female and 24 male patients (age, 15.7 ± 3.2 years). Defect size decreased (P <.001) in all 3 directions (medial-lateral × anterior-posterior × depth) at 29 ± 9.0 months: preoperatively, 7.9 ± 2.8 × 8.0 ± 3.2 × 4.1 ± 1.5 mm; postoperatively, 3.5 ± 3.3 × 4.0 ± 3.5 × 1.6 ± 1.4 mm. Healing of the subchondral bone was graded as good in 19 defects (35%), fair in 27 (50%), and poor in 8 (15%). The mean postoperative OES score was 40 ± 8.4. Neither postoperative defect size nor healing grade correlated with the OES (P >.05). Conclusion: Arthroscopic debridement and microfracture for advanced capitellar OCD result in improved (ie, decreased) defect size at a mean follow-up of 29 months, both in width and in depth. Healing of the subchondral bone was either good or fair in 85%. Interestingly, CT findings did not correlate with clinical outcomes.