This study takes a quality assurance approach to assessing staff application of Paris System recommendations for brachytherapy. Between 1988 and 1992, 72 patients were treated with brachytherapy for cancer of the lip at Hospital Clinic in Barcelona. Because of the relatively high number of total local recurrences (11%) and the fact that several radiotherapists had come from other hospitals to join the staff, we analysed the technique actually used compared with the recommendations of the Paris System. Results indicate our staff did not, in fact, use the active length prescribed by the Paris System in 71% of cases but that the discrepancies had no observable impact on the actuarial local control in the short follow-up period (28 +/- 15 months). When we compared, in time sequence, the first 35 patients treated between 1988 and 1989 (Early group) with the last 37 treated between 1990 and 1992 (Later group), we saw that staff members had improved their application of the therapy by more often using the recommended length of active lines. Staff performance in the Later group was still far from ideal, however, as the actual length used differed from the length recommended in 51% of the cases. At present we are insisting on stricter application of the Paris System guidelines for lip brachytherapy. Our study suggests that auditing performance is worthwhile and we recommend that radiotherapists apply this analytical quality assurance method, especially when several new physicians join a department.