To investigate the long-term predictive value of urodynamics for the outcome of patients undergoing prostatic surgery for lower urinary tract symptoms (LUTS) suggestive of bladder outlet obstruction (BOO) and to determine the long-term effectiveness on symptoms, maximum flow rate and the rate of re-operation. Of 139 elderly men who had undergone prostatic surgery, selected without reference to urodynamic assessment but having extensive (blinded) urodynamic testing included in their evaluation, 79 were followed for 8 years using a history, symptom score analysis, uroflowmetry and review of their records. Comparing the results in groups of men with a pre-operative maximum flow rate < or > or = 15 mL/s, there was a similar difference in the rate of success to that noted 6 months post-operatively. Similar results were obtained when comparing those with BOO or a normal bladder outlet function. However, although the tendency was clear it was not statistically significant because of the small sample size (type-2 error). There was a significant reduction in all symptom scores from those assessed pre-operatively and during the 8 years (P < 0.001). The median pre-operative maximum flow rate was 8.5 mL/s, compared with 12.5 mL/s after 8 years (P < 0.001). Of the 79 patients, 14 (18%) had 28 re-operations during the 8-year follow-up, 12 being repeat resections of the prostate, giving a repeat resection rate of 1.8% per year and a success rate of 71%. During the 8 years, 82% of the patients had an unchanged overall evaluation of the post-operative outcome. In general, those having an unsatisfactory outcome were slightly younger than the whole group. Uroflowmetry and pressure-flow studies can predict to some degree the long-term result after prostatic surgery. There was a durable effect on symptom scores and maximum flow rates after the operation. The annual rate of repeat resection (1.8%) was relatively low.