Overactive bladder (OAB) is a common symptom syndrome with urgency, urinary frequency, and urgency incontinence. To collectively express OAB symptoms, we developed the overactive bladder symptom score (OABSS). Four symptoms--daytime frequency, nighttime frequency, urgency, and urgency incontinence--were scored. The weighing score was based on a secondary analysis of an epidemiologic database. Psychometric properties were examined in five patient groups: OAB (n = 83), asymptomatic controls (n = 34), stress incontinence (n = 29), benign prostatic hyperplasia (n = 28), and other diseases with urinary symptoms (n = 26). The maximal score was defined as 2, 3, 5, and 5 for daytime frequency, nighttime frequency, urgency, and urgency incontinence, respectively. The sum score (OABSS 0 to 15) was significantly greater in the patients with OAB (8.36) than in the other patient groups (1.82 to 5.14). The distribution of the OABSS showed a clear separation between those with OAB and asymptomatic controls. The OABSS correlated positively with the individual scores (Spearman's r = 0.10 to 0.78) and quality-of-life scores assessed by the King's Health Questionnaire (Spearman's r = 0.20 to 0.49). The weighted kappa coefficients were 0.804 to 1.0 for each symptom score and 0.861 for OABSS. The posttreatment reduction in the OABSS was consistent with the global impression of patients of the therapeutic efficacy. The OABSS, the sum score of four symptoms (daytime frequency, nighttime frequency, urgency, and urgency incontinence), has been developed and validated. OABSS may be a useful tool for research and clinical practice.