There have been several investigations reporting on urinary retention in postpartum women who delivered vaginally with epidural blockade. The mechanism and incidence of urinary retention in relation to epidural analgesia, however, are not established. The objectives of this study were to investigate the association between various obstetric parameters and urinary retention and to determine whether those women with postpartum urinary retention subsequently develop urinary problems. From December 1999 to September 2000, 110 primiparas who delivered vaginally with epidural analgesia for labor pain relief were recruited prospectively. One hundred primiparas delivering under similar conditions without epidural analgesia were selected as the control group. Residual urine volume was calculated by trans-abdominal sonogram. A computerized obstetric database was analysed to compare the two groups. Women with epidural analgesia, especially those with residual volume exceeding 500 ml, had significantly longer labor course, a higher percentage of instrumental deliveries and more extensive vaginal or perineal lacerations than the control group. Only a few women had persistent problems with micturition six months after delivery. Epidural analgesia provides valuable pain relief but may be associated with greater residual urine. Postpartum urinary retention is, however, more related to prolonged labor than to the effect of epidural analgesia itself. Close monitoring of the progress of labor and avoiding urine retention are essential.