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Case summary An 8-year-old male neutered domestic shorthair cat was presented with an acute onset of left thoracic limb lameness and a firm swelling on the lateral aspect of the left distal antebrachium. A CT scan of the left thoracic limb revealed an expansile osteolytic cystic bone lesion centred at the distal left ulnar metaphysis. Cytology from fine-needle aspiration was not consistent with neoplasia. The CT features and the cytology results were suggestive of a bone cyst. A distal partial ulnectomy with ulnar styloid process excision was performed as the biopsy method and as the treatment approach. Histopathology results were consistent with an aneurysmal bone cyst (ABC). Carpal instability was not detected after distal partial ulnectomy; therefore, a stabilisation method was not required. Limb function was excellent after surgery, with no lameness and no recurrence detected by the owner at 2, 6 and 24 weeks postoperatively. The veterinary examination at 12 weeks postoperatively confirmed the owner’s outcome assessment. Relevance and novel information To the authors’ knowledge, this is the first report describing a distal partial ulnectomy with ulnar styloid process excision in a cat. Despite disrupting the short ulnar collateral ligament, this technique provided excellent short-term limb function with no need for carpal joint stabilisation. This technique allowed for the complete excision of a distal ulnar ABC and avoided cyst debridement, which could be associated with haemorrhage, recurrence and malignant transformation. Distal partial ulnectomy should be considered for distal ulnar bone lesions in cats.