Case summary A 5-year-old male neutered cat weighing 3.56 kg presented owing to the development of two masses over the dorsal cervical and cranial thoracic areas, as well as weight loss, inappetence and vomiting. Diagnostic tests revealed a grossly lipaemic sample with hypercholesterolaemia (440 mg/dl; reference interval [RI] 90.0–205.0), hypercalcaemia (>16.0 mg/dl [RI 8.0–11.8]) and urine specific gravity 1.022 (RI ⩾1.035). When re-presented 9 months later, fasted blood analyses revealed elevated ionised calcium (1.87 mmol/l [RI 1.11–1.38]), persistently elevated total calcium, normal phosphate and persistent minimally concentrated urine with calcium oxalate dihydrate crystals. Ultrasound-guided fine-needle aspiration of the masses produced blood-tinged purulent fluid with negative culture results. Excisional biopsies of both masses were undertaken, and histopathology was consistent with cutaneous xanthoma. No organisms were identified with special staining, and deep-tissue culture did not grow bacteria or fungi. Postoperatively, repeat fasted biochemical analysis revealed persistent hypercholesterolaemia with normal triglycerides, and normalisation of ionised and total calcium levels. Based on these findings, a diagnosis of cutaneous xanthoma causing hypercalcaemia due to primary dyslipidaemia was made. The cat was reported to be significantly improved in comfort and energy levels postoperatively and a transition to a fat-restricted diet was instituted. Eight months after xanthoma removal no recurrence was reported. Relevance and novel information To our knowledge, this is the first report of cutaneous xanthoma and associated granulomatous inflammation causing hypercalcaemia due to dyslipidaemia in a cat. Familial hypercholesterolaemia is an example of a primary condition that could cause dyslipidaemia in cats, and further studies are warranted to better describe the genetic characteristics. Xanthoma formation and the resultant granulomatous inflammation should be considered in cases of hypercalcaemia.