The efficacy and safety of the routine use of target-controlled infusion of propofol for the sedation of patients undergoing transrectal ultrasound-guided prostate biopsy were assessed. The optimal level of sedation was also evaluated. A total of 250 patients were randomized into five groups according to sedation level determined by the Observer's Assessment of Alertness/Sedation (OAA/S) scale. As the level of sedation was increased, the overall pain and discomfort score decreased and the satisfaction rate tended to increase, although hypoxia meant that intervention occurred more frequently at higher sedation levels. Target-controlled infusion of propofol provided safe and effective sedation during transrectal ultrasound-guided prostate biopsy, particularly if moderate sedation (OAA/S score of 3) was achieved. The effect-site concentration of propofol for this level of sedation was about 1.5 µg/ml.