There is a documented association between diffuse planar xanthoma and chronic myelomonocytic leukemia. Previous accounts have hypothesized that patients with multiple lesions or extensive cutaneous disease are more likely to have an underlying abnormality of the reticuloendothelial system. However, we document a 62-year-old woman with a large pruritic yellow-orange plaque on the chest and lower anterior neck consistent with planar xanthoma that was discovered to have chronic myelomonocytic leukemia. Solitary large plaques of planar xanthoma should be considered in the same fashion as diffuse planar xanthoma and warrant a prompt hematologic evaluation.