The advent of positron emission tomography (PET) and PET/computed tomography (CT) now enables us to detect metabolically active gynecologic cancers with greater accuracy than was possible with anatomic imagings. Fluorine-18 fluorodeoxyglucose PET has been useful in differentiation of malignant from benign lymph nodes, and residual or recurrent cancers from post-treatment changes. PET/CT produces additional information for the diagnosis and tissue biopsy as well as radiotherapy planning. This paper reviews the principle and clinical utility of PET and PET/CT in the diagnosis, staging, recurrence, therapeutic response as well as prognosis of gynecologic cancers.