Background: The value of [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) uptake in endometriosis has not yet been extensively reported. Case report: A 32-year-old woman was examined to find an explanation for right pelvic pain associated with right subcostal pain. A computerised tomography (CT) scan was compatible with a haemangioma or a focus of endometriosis in the liver. Transvaginal sonography and magnetic resonance imaging (MRI) showed a complex ovarian cyst on the left. Blood CA125 levels were elevated. FDGPET revealed a focus of uptake in the right paravesical area. Laparoscopy showed a left endometrioma associated with diffuse inflammatory pelvic adhesions. After surgery and 3 months GnRH agonist treatment the pain had disappeared and neither MRI nor FDGPET showed any pelvic abnormality. The patient subsequently presented with dyspareunia and rectal pain resulting from a right uterosacral nodule and a rectal nodule. These were resected laparoscopically. After a 1-year followup, the patient is doing well. Conclusion: Endometriosis can give rise to falsepositive results on FDGPET. However, the FDG uptake in this particular case of endometriosis seems to have been due to inflammation rather than to a cyst. This report highlights the relationship between some of the biological features of endometriosis and some observed in neoplastic lesions. Background: The value of [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) uptake in endometriosis has not yet been extensively reported. Case report: A 32-year-old woman was examined to find an explanation for right pelvic pain associated with right subcultal pain. A computerized tomography (CT) scan was compatible with a haemangioma or a focus of endometriosis in the liver. Transvaginal sonography and magnetic resonance imaging (MRI) showed a complex ovarian cyst on the left. Blood CA125 levels were elevated. PET revealed a focus of uptake in the right paravesical area. Laparoscopy showed a left endometrioma associated with diffuse inflammatory pelvic adhesions. After surgery and 3 months GnRH agonist treatment the pain had disappeared and neither MRI nor FDG-PET showed any pelvic abnormality. The patient further presented with dyspareunia and rectal pain resulting from a right uterosacral nodule and a rectal nodule. These were resected laparoscopically. Aft er a 1-year follow-up, the patient is doing well. Conclusion: Endometriosis can give rise to false-positive results on FDG PET. However, the FDG uptake in this particular case of endometriosis seems to have been due to inflammation rather than to a cyst. This report highlights the relationship between some of the biological features of endometriosis and some observed in neoplastic lesions.