Background: It is unknown whether unstable chondral lesions observed during arthroscopic partial meniscectomy (APM) require treatment. We examined differences at 1 year with respect to knee pain and other outcomes between patients who had debridement (CL-Deb) and those who had observation (CL-noDeb) of unstable chondral lesions encountered during APM. Methods: Patients who were >= 30 years old and undergoing APM were randomized to receive debridement (CL-Deb group; n = 98) or observation (CL-noDeb; n = 92) of unstable Outerbridge grade-II, III, or IV chondral lesions. Outcomes were evaluated preoperatively and at 8 to 12 days, 6 weeks, 3 months, 6 months, and 1 year postoperatively. Outcome measures included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), visual analog scale (VAS) pain score, Short Form-36 (SF-36) health survey, range of motion, quadriceps circumference, and effusion. The primary outcome was the WOMAC pain score at 1 year. T tests were used to examine group differences in outcomes, and the means and standard deviations are reported. Results: There were no significant differences between the groups with respect to any of the 1-year outcome scores. Compared with the CL-Deb group, the CL-noDeb group had improvement in the KOOS quality-of-life (p = 0.04) and SF-36 physical functioning scores (p = 0.01) as well as increased quadriceps circumference at 8 to 12 days (p = 0.02); had improvement in the pain score on the WOMAC (p = 0.02) and KOOS (p = 0.04) at 6 weeks; had improvement in SF-36 physical functioning scores at 3 months (p = 0.01); and had increased quadriceps circumference at 6 months (p = 0.02). Conclusions: Outcomes for the CL-Deb and CL-noDeb groups did not differ at 1 year postoperatively. This suggests that there is no benefit to arthroscopic debridement of unstable chondral lesions encountered during APM, and it is recommended that these lesions be left in situ.