This study investigated whether the enzyme telomerase is active in bladder tumours, whether there is any correlation between activity and grade, and whether the enzyme is expressed in non-malignant conditions. Fifty-two patients undergoing cystoscopy or TURBT at a district general hospital were included, 25 with current bladder tumours, 13 with previous but no current tumours, and 14 with non-malignant pathology. Specimens were analysed by the telomerase repeat amplification protocol (TRAP assay), a highly-sensitive polymerase chain reaction (PCR)-based assay, and a commercially-available ELISA kit. Telomerase activity was detected in 80% of bladder tumours, more frequently in moderate- or poorly-differentiated (93%) than well-differentiated (56%) tumours. Activity was not uniform across individual tumours. Telomerase was also frequently (61%) detected in inflammatory lesions found in patients being followed up for previous bladder tumours, and in two (14%) patients with benign pathologies. In conclusion, telomerase was frequently but not uniformly detected in bladder tumours; its presence was not specific to malignancy. There is a possible correlation between tumour grade and telomerase activity.