Urological pathology causing free air under the diaphragm?

We report a case of long-standing, keratinising, squamous metaplasia of the bladder with undiagnosed malignant transformation to squamous cell carcinoma presenting as acute peritonitis secondary to spontaneous perforation of the bladder tumour. This presentation as an acute abdomen mimicking a perforated peptic or duodenal ulcer is the most unusual aspect of the case.