A 72-year-old woman, who was otherwise healthy, developed a painful ulceration on her right lower extremity after minor trauma. The ulcer started as a small pustule on her right leg and rapidly evolved into a painful ulcer. Initial investigation revealed normal laboratory test results with the exception of an elevated white blood cell count (66.0 × 103/µL [reference range, 4.5-11.0 × 103/µL]). Subsequent workup revealed chronic myelomonocytic leukemia, with multiple complex cytogenetic findings, including a 5q– mutation and an absence of the Philadelphia chromosome. Before her hospitalization, the patient underwent surgical debridement, which led to rapid progression of her ulcer and aggravation of her pain.