The objective of this study was to describe client-assessed long-term functional outcome following surgical site infection (SSI) in dogs that underwent tibial plateau levelling osteotomy (TPLO) and identify predictive factors for infection development and management. This study is a retrospective clinical case series. Clinical records of dogs (n=545) undergoing TPLO surgery (n=683) were reviewed. Signalment, clinical details, surgical management and postoperative complications were recorded. Multilevel analysis was used to assess the relationship between signalment and clinical variables and the subsequent development of SSI. Additionally, SSIs were analysed to identify predictors for management. Long-term functional outcome was evaluated using a previously validated clinical metrology instrument (Liverpool Osteoarthritis in Dogs (LOAD) questionnaire). SSI occurred in 4.7 per cent (95 per cent CI 3.3 per cent to 6.5 per cent) procedures. Of the dogs with SSI, 37.5 per cent required implant retrieval and later onset SSI was associated with increased requirement for retrieval (P=0.04). There was no significant difference in LOAD score (P=0.7) in dogs with or without SSI. Crossbreed dogs had a lower risk of developing SSI (P=0.03). There was no association between SSI and long-term functional outcome (as assessed by LOAD) in dogs following TPLO. Later onset of SSI is more likely to require implant retrieval to resolve. Crossbreed dogs may be at reduced risk of developing SSI.