In 477 patients with superficial bladder tumours Ta or T1 the frequency of tumour recurrence was studied and related to histological grading and presence of single or multiple tumours. Furthermore the DNA pattern was studied in 222 out of these cases and again related to the rate of recurrence. An overall recurrence rate of 71% was found. A threefold increase of the mean annual recurrence rate was found comparing single with multiple (0.42 and 1.22) G1 with G2 (0.28 and 0.87) and diploid with aneuploid tumours (0.52 and 1.54). The highest frequency of annual recurrences of 1.70 was found in the aneuploid tumours with near triploid DNA pattern. This value is close to that of 1.76 found in cases who died from progressive cancer disease.