Abstract: A 6-year-old female spayed Boxer mix dog was presented with multiple cutaneous masses, one of which was determined to be a xanthoma. Fine-needle aspirates of this mass revealed large round cells that were consistent with macrophages. These macrophages had lightly basophilic cytoplasm that was filled with many clear circular spaces that varied in size. The nuclei of these cells displayed mild anisokaryosis with condensed chromatin and lacked prominent nucleoli. The cytologic interpretation was lipid-laden histiocytic inflammation most consistent with a cutaneous xanthoma, which was confirmed histologically. Mild hypertriglyceridemia and persistent moderate hypercholesterolemia were present. After ruling out other causes of hyperlipidemia, we concluded that the dog likely had idiopathic hyperlipidemia with secondary xanthoma formation.