We present a 43-year-old male, who was admitted with the diagnosis of Adult-onset Still's disease, after several months of arthralgias, febricula and loss of weight. Chest x-ray, abdominal ultrasonography, chest, abdomen and pelvic CT scan and bone scintigraphy were performed. Scintigraphic findings oriented to the performance of a bone marrow biopsy with diagnosis of acute lymphoblastic leukemia.