Development of lysis within an area of pagetic bone suggests a sarcoma. We report the case of a 61-year-old woman who had increasingly severe pain in her right hip and a decline in general health. The roentgenogram of the pelvis showed previously known pagetic lesions of the right half of the pelvis and osteolysis of the roof of the acetabulum. Additional imaging studies (ultrasonography, computed tomography, and magnetic resonance imaging) disclosed a pelvic tumor extending on either side of the right ilium. The peripheral white blood cell count was markedly elevated (93,000/mm3) as a result of inappropriate secretion of granulocyte-colony-stimulating factor. The tumor was an anaplastic large cell lymphoma of T-cell origin with CD30 positivity, i.e., a Ki-1 lymphoma. Most CD30-positive lymphomas are high-grade tumors. There has been only one previous report of Ki-1 lymphoma with production of granulocyte-colony-stimulating factor and hyperleukocytosis. It has been suggested that cytokines may influence tumor growth. Unusual features in our case include development of the Ki-1 lymphoma in an area of pagetic bone and presence of a leukemic syndrome due to increased production of a growth factor.