Bone lesions of Kaposi sarcoma are rare. A 56-year-old man who was HIV positive and was diagnosed with Kaposi sarcoma on the basis of the results of a biopsy of skin lesions, underwent F-18 FDG PET/CT scan for detecting Kaposi sarcoma lesions and other AIDS-related diseases. An abnormal uptake was observed in the lumbar spine. MRI showed a diffuse enhanced spine lesion, and Ga-67 and ²⁰¹Tl scanning were negative. As a result, the lesion was considered to be a Kaposi sarcoma, and the shrinkage of the lesion was noted after the therapy for Kaposi sarcoma.