[en] Full text: The management of the patients with carcinoma of an unknown primary represents a difficult challenge in oncology. Metastatic cancers of unknown primary origin are characterised by a poor prognosis. Conventional radiological imaging allows only detection of 20%-27% of primary cancers. To evaluate the role of ¹⁸F-FDG PET/CT in detection of primary tumors in carcinoma of unknown primary site. Methods: In the present study, a total of 31 patients (22 males, 9 females; mean age 53.1 years) with biopsy or cytopathology proven metastatic carcinoma and negative conventional diagnostic procedures (CT, MRI or Panendoscopy) were included. All patients underwent whole body ¹⁸F-FDG PET/CT study. Patient data was retrospectively analysed. Histopathological diagnosis is kept as the gold standard. Hypermetabolic areas at the site of CT changes were considered as positive and rate of detection of primary site is evaluated. Among 31 patients, ¹⁸F-FDG PET/CT detected primary site in 14 patients. ¹⁸F-FDG PET/CT was negative in remaining 17 patients and could not localise primary. Among the 14 positive PET-CT patients, the results of 2 patients became false positive. The detection rate of ¹⁸F-FDG PET/CT in localising primary site was 38%. It is concluded that ¹⁸F-FDG PET/CT was found to be useful diagnostic procedure for the evaluation of patients with metastatic carcinoma and primary of unknown origin