Abstract OBJECTIVE To report and evaluate the risk factors for complications following bi-oblique proximal ulnar osteotomy (PUO) in dogs. ANIMALS 82 client-owned dogs (93 limbs). METHODS Clinical records of dogs treated with bi-oblique PUO over a 5-year period were reviewed. Postoperative radiographs were analyzed, and osteotomy location and angles were recorded; follow-up radiographs were reviewed to assess the degree of osteotomy healing. Complications were classified as minor, major, and catastrophic. Logistic regression analysis was performed to investigate possible associations between the predictor variables and occurrence of complications. RESULTS 82 dogs (93 limbs) were included. Postoperative complications were documented in 39 limbs (13 major and 26 minor). The most common major complication was osteotomy nonunion (8 limbs), while the most common minor complication was delayed union (21 limbs). Statistical analysis revealed that lower body weight (P = .01) and older age (P = .04) were significantly associated with the development of postoperative complications. CLINICAL RELEVANCE In this study, lighter and older dogs were more likely to develop complications following bi-oblique proximal ulnar osteotomy. We did not identify an association between osteotomy angle and location on complication rate. Careful patient selection is therefore required to reduce the incidence of postoperative complications after bi-oblique PUO.