OBJECTIVE: Evaluation of lameness and osteoarthritis (OA) progression following Tibial Plateau Leveling Osteotomy (TPLO) in dogs with naturally-occurring rupture of the cranial cruciate ligament (CCL) and investigation of factors with potential influence on long-term outcome. MATERIAL AND METHODS: In a retrospective clinical study medical records of 119 client-owned dogs (135 operated stifle joints) and corresponding client-questionnaires were reviewed, collecting data on radiologic and surgery results, course of surgery and complications. In a check-up, orthopaedic examination and stifle radiographs were performed to assess status quo of OA, lameness, and progression of OA. RESULTS: 58 dogs (66 stifle joints) could be examined clinically and radiologically, whereas 61 dogs (69 stifle joints) were re-checked by client-questionnaire only. Up to 6.8 years after TPLO surgery, in 90.4% of all cases lameness results were judged "excellent" (n=84) or "good" (n=38). In the long term, there was a moderate but significant progression of OA following TPLO surgery. Patients with totally ruptured CCL were significantly more likely to have meniscal injury than dogs with partially ruptured CCL. Dogs with partial meniscectomy had a significantly higher rate of "excellent" long-term clinical results and less frequently showed progression of OA compared to those having the meniscus released or left untouched. The overall complication rate was 22.2% (n=30), with the type of complication having no influence on the long-term clinical outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Regarding lameness, the long-term outcome following TPLO is very satisfying. Early surgical treatment of CCL rupture using TPLO can help to decrease the likelihood of OA progression. Partial medial meniscectomy may help to avoid repeated surgery due to subsequent meniscal injury without having a negative impact on long-term functional outcome or the progression of OA in the affected joint. Neither long-term clinical results, especially regarding lameness, nor OA were impaired by previous surgery prior to TPLO or the occurrence of complications associated with TPLO surgery.