Objectives. To examine the test-retest reliability and the validity of a voiding diary designed to assess the symptoms of frequency, urgency, and urge urinary incontinence (UI).Voiding diaries serve as the primary tool to assess symptoms of overactive bladder in clinical settings and in clinical trials of treatment for overactive bladder. Despite the widespread use of these instruments, few studies have documented their measurement properties or investigated the number of days required to assess symptoms accurately. Methods. Study participants included 21 men and 133 women at least 20 years of age recruited from urogynecology and urology clinics. All had a history of urge incontinence or mixed incontinence with urge as the primary component. Participants completed a 7-day voiding diary on two occasions, separated by at least 1 week. Results. Men and women reported a daily average of approximately 10 micturitions, 7 occurrences of strong urge, and 2 episodes of urge urinary incontinence. The diary exhibited good to excellent reliability, with estimated intraclass correlation coefficients (ICCs) ranging from 0.81 to 0.86 for the symptoms of strong urge, diurnal and nocturnal micturitions, total incontinence, and urge incontinence episodes. Estimates did not differ appreciably between men and women. Moderate correlations with global questions on micturition frequency and UI episodes supported the validity of the diary. Diaries completed for 3 and 4 days were similar, with only slightly lower estimates of reliability (ICC 0.79 to 0.84). Conclusions. The voiding diary completed for 7 days, following detailed instruction, is reliable and appears to be valid for documenting the change in symptoms of overactive bladder in men and women with predominantly urge incontinence. Because of comparable reliability and reduced patient burden, diaries of shorter duration may also be acceptable to assess the symptoms of overactive bladder, depending on the degree of precision required. © 2003, Elsevier Science Inc.