We describe here a 65-year-old woman with a right-sided ureteral tumour that was treated by nephroureterectomy. The tumour appeared to be a signet-ring cell carcinoma obstructing the lumen and infiltrating the whole thickness of the ureteral wall. No other primary site could be found, and the tumour is believed to represent the first reported case of primary signet-ring cell carcinoma of the ureter.