Neoplasms arising from the urachus are extremely rare. We present a case of a young woman with mild abdominal pain and a palpable swelling in the mid abdomen with incidental detection of a subumbilical mass. Repeated fine-needle aspiration cytology failed to reveal the true nature of the lesion. 18F-FDG PET/CT showed tracer uptake in the cranial end of urachal remnant lesion. Core biopsy from the site with maximal FDG uptake turned out to be lymphomatous involvement in urachus, which is extremely rare and previously unreported.