A 50-year-old man with advanced inoperable gastric adenocarcinoma and diffuse peritoneal metastasis received six cycles of palliative chemotherapy and responded clinically with weight gain. Two months after the completion of chemotherapy, however, he developed a left hydrocele. Aspiration yielded 70 ml of yellowish hydrocele fluid, which contained metastatic adenocarcinoma cells, consistent with a gastric primary tumour. A diagnosis of malignant hydrocele was made. Two weeks later, he developed a painful recurrent left hydrocele with increasing pain and swelling. Left orchidectomy was performed. Tiny white mural nodules measuring 1 mm in size were noted on the tunica vaginalis. No focal lesion was noted in the testis. On microscopic examination, the tunica vaginalis showed reactive mesothelial hyperplasia and extensive lymphatic permeation by poorly differentiated adenocarcinoma, consistent with a gastric primary tumour.