Overactive bladder (OAB) is a common health problem in women and tends to increase with age. Although OAB symptoms can occur due to involuntary detruosr contractions and incomplete bladder emptying, incomplete bladder emptying in older women who have OAB symptoms has been given little attention by researchers. Detrusor underactivity (DUA) and bladder outlet obstruction (BOO) have been proposed as causes of incomplete bladder emptying but research about the risk factors related to incomplete bladder emptying in exclusively older women is still scant. Therefore, the purpose of this study was to examine the relationship between risk factors of DUA and BOO and incomplete bladder emptying in women aged 65 or older who have OAB symptoms. A total of 203 medical records were reviewed and 170 met the inclusion criteria. Model selection was conducted to determine the best model for analyzing the data. Logistic regression and a receiver operator characteristics (ROC) curve were performed to answer the research questions. Sixty-six (39%) of the women had incomplete bladder emptying. The result revealed a significant relationship between the presence of diabetes mellitus and increased bladder capacity ([greater than or equal to]500ml) and incomplete bladder emptying. Another significant but unexpected relationship was found between anterior vaginal prolapse and incomplete bladder emptying: an increase in the degree of anterior vaginal prolapse decreased the risk of incomplete bladder emptying. However, the relationship between incomplete bladder emptying and urinary frequency was not significant. Among urodynamic parameters, a maximal urine flow rate (Qmax) and voiding patterns were significantly related to incomplete bladder emptying: a greater maximal urine flow rate (Qmax) and interrupted voiding pattern were associated with an increased risk of incomplete bladder emptying. The current study raises awareness of incomplete bladder emptying in older women with OAB symptoms. In addition, the findings may help nurse researchers and health care professionals understand what risk factors are related to incomplete bladder emptying in older women who have OAB symptoms.