OBJECTIVES To report short- and long-term outcomes after arthroscopic treatment in young large breed dogs affected by medial coronoid process disease (MCPD) and identify variables affecting outcome. STUDY DESIGN Prospective observational case series. ANIMALS Large breed dogs <3 years old (n = 15; 23 elbows). METHODS MCPD was confirmed by radiography, computed tomography, and arthroscopy. Dogs were treated by arthroscopy. Variables recorded at time of treatment included radioulnar incongruity (RUI) and degree of cartilage erosion. Variables recorded before, 6 weeks, and ≥23 months after surgery included radiographic score for osteoarthritis, trochlear notch sclerosis, muscle circumference, range of motion (ROM), and the load distribution of vertical ground reaction forces between thoracic and pelvic limbs. RESULTS A greater load distribution to the pelvic limbs was identified preoperatively in dogs with RUI than in dogs with congruent elbows. Load distribution was not significantly improved at 6 weeks compared with preoperatively. Muscle circumference and vertical impulse distributions were improved at long-term evaluation despite an increased osteoarthritis score. This improvement was more obvious in dogs with RUI or a high degree of cartilage erosion at initial presentation. CONCLUSION Some evidence of improvement in long-term function was found in dogs with MCPD after arthroscopic treatment. RUI and cartilage erosion at the time of diagnosis were associated with more lameness preoperatively but did not affect the final gait assessment or osteoarthritis score in this small cohort.