FDG-PET/CT detected an incidental seminoma testis in a NF1-patient with simultaneous hypermetabolic thoraco-abdomino-pelvic lesions, which were first attributed to the seminoma, then considered to be sarcoid-like lesions according to histology, and were ultimately diagnosed as syphilitic granulomas based on serology and functional imaging before and after antibiotic treatment. Here, NF1 is linked to seminoma.