OBJECTIVE To determine if hexylaminolaevulinate fluorescence cystoscopy (HAL-FC) has the potential to improve the diagnosis of bladder cancer in patients who have been treated with bacille Calmette-Guérin (BCG). PATIENTS AND METHODS Patients scheduled for rigid cystoscopy after BCG therapy were recruited prospectively between April 2005 and February 2006. Patients received HAL (Hexvix, PhotoCure ASA, Oslo, Norway) and the D-light system (Storz, Tuttlingen, Germany) was used to detect fluorescence. The bladder was mapped and biopsies taken under white light and then using HAL-FC. The main outcome was the frequency and nature of additional pathology detected by HAL-FC. Twenty-seven patients (21 men and six women; median age 70 years, range 49-82) underwent 32 HAL-FC. RESULTS Recurrent bladder cancer was detected in 11 of the 32 (34%) examinations. HAL-FC detected additional pathology in five of the 27 (19%) patients. In two of these cases the additional pathology was clinically significant (one pT4G3 intraprostatic transitional cell carcinoma and one intravesical pT1G2 + carcinoma in situ), whereas in three cases the pathology was hyperplasia/dysplasia. Overall, the false-positive biopsy rate with HAL-FC was 63%. In the presence of positive voided urine cytology six of eight patients had recurrent bladder tumour and the false-positive biopsy rate was only 34%. Urine cytology was positive in four of five of the patients in whom additional pathology was detected by HAL-FC. CONCLUSIONS Clinically significant occult pathology can be detected using HAL-FC after BCG therapy, but in <10% of cases. The rate of false-positive biopsies is high but in our hands appears to be lower than with white-light guided biopsies after BCG. Our pragmatic approach is to use HAL-FC after BCG when clinical suspicion is high, and when the preoperative voided urine cytology is positive.