Uroflowmetry and the American Urological Association symptom index (AUASI) are often used clinically to evaluate patients with benign prostatic hyperplasia (BPH). Since results from these tests may be used to determine a treatment course, including surgical intervention, we investigated if specific combinations of uroflowmetry and AUASI parameters could better predict urodynamically confirmed prostatic obstruction. Data from 134 men (mean age: 67.8 +/- 8.9 years) with prostatism were analyzed. The patients underwent uroflowmetry in the standing position after completing the AUASI; the post-void residual volume (PVR) was determined. The presence and severity of prostatic obstruction was assessed by video urodynamics, which included micturitional urethral pressure profilometry (MUPP). Of the 134 total patients, 66 were found to be obstructed by MUPP. Correlations of maximum urinary flow rate (Qmax), PVR, and AUASI with the degree of obstruction were poor and not substantially improved using combinations of these parameters. Threshold values of Qmax and AUASI, when used in combination, allowed accurate prediction of obstruction or non-obstruction in a small subset of the patient population. Of 14 men with both Qmax < 10 ml/s and AUASI > or = 20, 13 were obstructed (specificity = 98%). Eight of 9 men with both Qmax > or = 15 ml/s and AUASI < 10 were non-obstructed. The combined Qmax and AUASI criteria categorized only 20% of the patients as obstructed or non-obstructed. Once other causes of urinary dysfunction are ruled out, use of these criteria will enable the urologist to make an accurate diagnosis of obstruction, select a treatment more likely to benefit the patient, and make further diagnostic testing unnecessary in this small subset of patients. In a large volume clinical practice of adult male voiding dysfunctions, diagnosis of even this small proportion of patients using this simple approach can reduce patient care costs.