OBJECTIVES: To evaluate the predictors of nocturia-related quality of life and to assess the early effect of prostatectomy on these parameters in patients with lower urinary tract symptoms suggestive of benign prostatic obstruction. METHODS: The study group included 56 consecutive patients scheduled for prostatectomy to treat medical treatment-refractory lower urinary tract symptoms. Nocturia severity was assessed preoperatively and 2 to 3 months after prostatectomy by the number of nocturia events, time from falling sleep to first awakening to void (hours of undisturbed sleep [HUS]), longest sleep interval between voids, and score on the nocturia quality-of-life (N-QOL) questionnaire (range 0 to 48). RESULTS: The mean age of the study group was 69 ± 9 years. The preoperative N-QOL score correlated strongly with the number of nocturia events, HUS, and longest sleep interval between voids (r = -0.69, r = 0.67, and r = 0.69, respectively, and P <0.001). Of the 56 patients, 36 (65%) underwent transurethral prostatectomy and 20 (35%) underwent open prostatectomy. Significant improvement (P <0.001) was noted in all factors after treatment. The number of nocturia events decreased from 3.4 ± 1.2 to 2.6 ± 0.99; the HUS increased from 1.83 ± 0.55 to 2.74 ± 0.64 hours; the longest sleep interval between voids increased from 2.36 ± 0.64 to 2.91 ± 0.6 hours; and the N-QOL score increased from 24.1 ± 7 to 34.4 ± 7.5. On multivariate stepwise regression analysis, the factors predicting for improvement in the N-QOL score after prostatectomy were the number of nocturia events and HUS. CONCLUSIONS: Prostatectomy is associated with an early postoperative improvement in nocturia indexes. The increases in the interval to first void and decrease in even less than one nocturia event were associated with significant improvement in nocturia quality of life.