Summary Even though the majority of patients with bladder malignancies initially present with low stage disease, the clinical epidemiology of these so-called superficial bladder tumours is not well known. In this paper, disease characteristics at initial presentation and during follow-up are described in 1,745 primary cases documented prospectively in the Netherlands. The risk of recurrent disease after primary treatment is very high: in 60% of cases, at least one recurrence is diagnosed within 5 years (95% CI: 58-62% Society, 1991). Therefore, the greatest concern in these patients is not to reduce mortality but to lower and postpone the number of recurrences (which are very common in superficial TCC) and thereby to prevent progression to invasive disease (and document) at least four random quadrant biopsies in macroscopically normal-looking urothelium (left and right lateral wall, trigone and dome) at the time of resection of the tumour(s). The therapy to be applied was transurethral resection of the tumour (TUR) in all patients. Urologists were advised to consider adjuvant intravesical instillations with chemotherapy or BCG vaccine in the case of multiple tumours. In pTI grade 3 patients more aggressive therapy, such as radical surgery or external or interstitial radiotherapy, would have to be considered. To detect recurrences, cystoscopy and urine cytology were used every 3 months in the first year after treatment. From the second year onwards, this check-up was performed every 6 months. Follow-up data concerning disease and life status were collected for each patient once every year.Between 1983 and 1990, 2,805 cases were documented. In 1991, all the data in the documentation project were reviewed using the medical files. After this check, the records of 100 cases were excluded. Of these, 30 had an inverted papilloma (which was considered to be benign), 58 had recurrent instead of primary disease at first registration, five did not have TCC in the bladder but in the upper urinary tract. In the records of seven cases, there were major inconsistences, which could not be corrected with information from the medical files. Of the remaining 2,705 cases, 1,745 (64.5%) had superficial TCC. 'Superficial' is defined as tumour extension limited to the mucosa (pTa) or the lamina propria (pTl) of the bladder wall with or without carcinoma in situ in random biopsies. In urology practice, primary carcinoma in situ (pTis) is considered to be very different from pTa and pTI tumours because of its relatively aggressive clinical behaviour. For that reason, patients with primary pTis (n = 52 in our series) were not evaluated in this study. Survival free of recurrence, survival free of progression and survival itself were measured from the data of histological diagnosis to the date of first recurrence, first evidence of disease progression and the date of death, respectively. Survival curves were based on the life table method, statistical significance being determined by the log rank test. The independence of host and tum...