Objective: To evaluate the clinical efficacy and safety of patient-controlled intravenous analgesia (PCIA) with fentanyl for cystospasm after transurethral resection of the prostate. Methods: Sixty benign prostatic hyperplasia (BPH) patients scheduled for transurethral resection of the prostate (TURP) under general anesthesia with laryngeal mask airway (LMA) were randomly divided into groups F and S. Group F (n=30) received PCIA device with fentanyl 10 μg/kg+8 mg ondansetron, and Group S (n=30) received placebo (PCIA device with 8 mg ondansetron). The visual analog scale (VAS) scores for pain were evaluated at 0, 2, 4, 8, 16, 24, and 48 h by the same staff. And recorded were incidence of cystospasm, side effects, application of hemostatic, duration of drawing Foley catheter and continuous bladder irrigation, time of exhaust after operation, time of post-operative stay and cost of hospitalization. Results: The incidence of cystospasm in Group F was significantly lower than that in Group S in the 48 h after operation (P