Objectives. There is debate about the validity of the clinical distinction between filling and voiding symptoms of benign prostatic hyperplasia (BPH). We examined empirically the evidence for the existence of these clinical constructs. Methods. We analyzed responses to the American Urological Association Symptom Index (AUA SI) among men from a large cohort sample (the Health Professionals Follow-up Study, n = 7753) and a subsample with physician-diagnosed BPH (n = 1856). We used factor analysis, which is a data reduction tool that allowed us to determine empirically the relationships among lower urinary tract symptoms thought to be clinically related by pathogenesis, physiology, or treatment response. Results. The results of the factor analysis indicated that responses to the AUA SI items could be grouped into one of two subscales: one describing voiding problems and the other describing filling problems. Analyses of internal consistency reliability indicated that the AUA SI as well as the filling and voiding subscales have sound internal reliability. Conclusions. We found empirical support for the clinical conceptualization of lower urinary tract symptoms into filling and voiding problems. These findings provide support for using the total score on the AUA SI as a reliable measure of overall symptom severity in BPH, as well as for separately summing the voiding and filling items to measure these distinctive types of lower urinary tract symptomatology. Further research is needed to determine whether these symptom groupings better distinguish responses to one treatment type over another. If so, targeting treatment based on the relative severity of voiding and filling symptoms might improve patient outcomes.