A 60-year-old woman presented after a fall and was noted to have ascites. She had a history of ulcerative colitis. History and physical examination did not reveal the likely aetiology of the ascites, but a sample showed it to be a blood-stained exudate. A malignant cause appeared likely, cross-sectional imaging was arranged and tumour markers sent. CA125 was 34 IU/ml (0-30); α-fetoprotein (AFP) and carcinoembryonic antigen (CEA) were normal. However, CA19-9 was 2880 U/ml (0-31). Pancreatic carcinoma or cholangiocarcinoma were of prime concern, but a CT scan and MRI imaging were normal. At laparoscopy a benign ruptured ovarian cyst was detected, and ascites drained. CA19-9 returned to normal and the patient remains well 9 months later. This case demonstrates how tumour markers may be misleading in the context of diagnostics, and is the highest reported example of CA19-9 rise in the context of benign ascites and benign ovarian pathology.