A malignant melanoma in the vagina is a rare entity, for which there is little evidence-based literature for guiding clinicians to understand the importance of disease staging via noninvasive imaging strategy. Conventional imaging techniques i.e. computed tomography (CT) may be suboptimal in evaluating a small volume tumour, which may lead to inaccurate staging of a loco-regional tumour. A multimodality imaging exploiting a glucose biomarker, i.e. 18 [F]FDG PET/CT, is being increasingly used for tumour staging, particularly when the other imaging modalities have failed, although its precise role in the T- staging remains to be defined. This paper reports a 51-year-old lady who presented with pervaginal bleeding for 3 months. She has no constitutional symptoms or history of bleeding tendency. Examination of the vagina revealed blood clots without discernible mucosal abnormalities. CT abdomen revealed no perceptible abnormalities aside for an asymmetry of the anterior vaginal fornices. A 18[F]-FDG PET/CT showed a focus of an FDG-avid lesion embedded in the right anterior vaginal fornix without lymphatic or distant metastasis. Histological sections of the tumour lesion confirmed the diagnosis of a primary malignant vaginal melanoma. This report documents the importance of FDG-PET/CT in delineating a small volume tumour which is imperceptible on CT imaging.