We have studied the accuracy of transabdominal ultrasound (TAUS) in the diagnosis of early superficial bladder carcinoma. One hundred and twenty-six patients returning for check cystoscopy were scanned pre-operatively with the Technicare Autosector Scanner and the results compared with the endoscopic findings. Forty-four patients (37%) had a tumour recurrence. TAUS demonstrated a lesion in 50% of these with a false positive rate of 11%. The diagnostic accuracy was proportional to the tumour size (82% of patients with tumours above 5 mm were detected compared with 38% below 5 mm), but was not affected by grade, stage or position in the bladder. TAUS may prove a useful adjunct to cytology as a screening test for bladder cancer.