OBJECTIVE: To evaluate the long-term clinical outcome in women with idiopathic detrusor overactivity (IDO) and to identify significant prognostic factors. DESIGN: Longitudinal study incorporating retrospective case note review and a postal questionnaire. SETTING: Tertiary referral urogynaecology clinic in Australia. POPULATION: Women with a sole urodynamic diagnosis of IDO. METHODS: Audit of urodynamic records and case notes. Postal questionnaire incorporating validated disease-specific quality-of-life (QoL) instruments. MAIN OUTCOME MEASURE: Subjective assessment of overall improvement on a 4-point scale followed by scoring of short forms of the urogenital distress inventory and incontinence impact questionnaire. RESULTS: One hundred and thirty two women were identified following examination of 1975 consecutive records with 76 (67%) returning questionnaires. Median follow up was 8 years (6-9), and the duration of symptoms was 13 years (9-18). Improvement was achieved in 25 (35%) women. Disease symptoms fluctuated in severity and QoL were worse in nonresponders to therapy (P < 0.0001). Urge incontinence at presentation was associated with treatment failure (P = 0.001) as was nocturia (P = 0.04), but urodynamic variables were not associated with outcome. Only 3 of 46 (6.5%) women not responding to therapy thought that their symptoms would improve with time. CONCLUSIONS: IDO seldom resolves and fluctuates in severity. Individual response is unpredictable, although the presence of urge incontinence is associated with a significantly worse prognosis.