Malignant melanoma has a high relapse rate, and PET is very useful for its detection, above all when its size is small or it is in locations that are difficult to resect. The radioguided surgery being implanted in many sites, new expectations are opening in these situations--the intraoperative location of the lesions by 18F-FDG and detection probe. This is a case report of a 44 years old woman diagnosed of malignant melanoma in her left leg 12 years ago. At present, she has a tumor in her left thigh, which was no longer palpable after a fine needle puncture was performed. This was reported as a mesenchymal tumor. Due to the possibility of recurrent melanoma, need for excision was suggested. In order to locate it, a PET-CT study with 18F-FDG was performed and the lesion was marked on the skin with the help of metallic points. The lesion was located in surgery with a gamma probe, showing relapse of melanoma. The importance of the case is found in the fact that it is the first step to extend the indications of radioguided surgery with the use of PET, a technique that offers a ride range of possibilities.