"Cold" lesions on bone scan have been reported in a variety of disease processes, including infection, avascular necrosis, and cysts. We present two cases of children who presented with large "cold" areas on technetium bone scans and were treated initially for septic processes. Acute childhood leukemia frequently presents with bone or joint pain, fever, and elevation of the erythrocyte sedimentation rate. Although the diagnosis may be difficult if the characteristic clinical signs and laboratory findings are absent, the presence of anemia should alert the physician to the possibility of malignancy. Bone scanning provides a sensitive method of localizing pathology, but diagnosis requires biopsy or marrow aspiration.