68Ga-PSMA PET/CT was performed in a 75-year-old man with newly diagnosed prostate cancer because of an equivocal lesion in the spine both on 99mTc-bone-SPECT/CT and MRI. Because of increased PSMA activity on PET/CT, the bone lesion was interpreted as metastasis from prostate cancer. Later, the patient was diagnosed as having monoclonal gammopathy of unknown significance. A biopsy was performed, and histological examination revealed multiple myeloma with PSMA expression in the neovessels but no metastatic prostate cancer cells. The patient was downstaged, and the treatment was changed accordingly. This case illustrates the importance of biopsies from PSMA PET–positive lesions.