OBJECTIVES: No measure has been available to assess the impact of recurrent genital herpes (RGH) outbreaks. Some herpes interventions attempt to abort an outbreak or reduce its length and/or severity. An instrument was required to determine the benefit of such interventions from the patients' perspective, in the context of a clinical trial. The objective was to develop a measure of the impact of outbreaks using items representing functional limitations of specific importance to RGH patients. METHODS: Content was derived via interviews with RGH patients (n = 40). Face & content validity of the draft HOIQ were assessed by cognitive de-briefing interviews with RGH patients (n = 19). Scaling/psychometric properties were assessed via a web-survey, whereby participants (n = 158) completed the HOIQ on two occasions during an outbreak, with 24 to 72 hours between administrations. RESULTS: Interviews revealed areas of functioning affected during an outbreak to include; social, work and other activities, relationships, personal hygiene, choice of clothing, need to avoid becoming tired, worry/anxiety and fear of discovery. De-briefing interviews indicated that content was appropriate and the measure easy to understand and complete. Rasch analysis of survey data yielded a 12-item unidimensional measure. Assessment of test-retest reliability was not possible due to rapid change in health status during an outbreak. However, item stability testing indicated that no items exhibited time-related differential item functioning, indicating reproducibility. Internal consistency was good (alpha: Time 1 = 0.87, Time 2 = 0.91). The HOIQ showed evidence of discriminative validity, being able to distinguish between individuals who differed according to self-reported severity of outbreak. CONCLUSIONS: The HOIQ represents an effective method for determining the impact of a herpes outbreak. The measure is scheduled to be used on a daily basis during such outbreaks in a trial designed to determine the effectiveness of a new treatment for RGH.