BACKGROUND Unilateral renal function often deteriorates with chronic ureteric obstruction. Our objectives were to determine the change in relative renal function (RRF) by MAG3 renography after intervention for ureteric obstruction, and to identify clinical/epidemiological factors which influence long-term outcomes. METHODS We identified 228 patients from 2006 to 2017 who underwent MAG3 renography before and after intervention for unilateral ureteric obstruction. Patients were grouped into categories preoperatively - with normal RRF (43-57%) through mild (29-42%), moderate (15-28%) and severe (<15%) impairment of RRF. Patient demographics, types of obstructive uropathy and intervention employed were analysed. Each group was assessed for the absolute change in RRF and change in RRF category postoperatively. RESULTS The mean patient age was 50.4 years (SD 16.7), and 62.3% were female. Overall, the mean pre- and post-intervention RRF of the obstructed kidney did not differ significantly (32.30% vs. 32.20%, P = 0.835). Most patients remained in their preoperative RRF group: 85.9% of normal, 67.4% of mild, 64.4% of moderate and 73.3% of patients with severe RRF impairment did not change category.Patients with mildly impaired preoperative RRF showed a significant worsening postoperatively (36.37% vs. 34.58%, P = 0.024). The other three groups showed no significant change in RRF following intervention.Multivariate logistic regression analysis showed no statistically significant association between type of intervention, age, gender or diagnosis and improvement in postoperative RRF category. CONCLUSIONS Our results show that RRF does not improve significantly after intervention for ureteric obstruction. The aim should therefore be to maintain existing renal function and relieve symptoms.