Rationalisation of follow-up in patients with non-invasive bladder tumours. A preliminary report. The risk of recurrence and progression in 170 patients presenting with pTa urothelial tumours of the bladder has been estimated so that follow-up can be rationalised. Patients were followed up for between 1 and 15 years, the original pathology reviewed and those with carcinoma in situ (CIS) or dysplasia of the background urothelium excluded. Only 5 patients progressed over the whole follow-up period, giving an overall progression rate of 3%. Solitary tumours had an annual initial recurrence risk (AIR) of 0.23 in the first year; after the first year the AIR fell to approximately 0.1 but did not fall significantly in subsequent years up to 8 years. Of the 45 patients with multiple tumours, 32 suffered recurrences within the first year (AIR 0.71). Tumour grade did not influence either recurrence or progression. The results indicate that for solitary pTa tumours, less frequent endoscopic follow-up is justified but some continued surveillance after 5 disease-free years is necessary. The estimated risk of recurrence is a useful factor to consider when planning follow-up. 