BACKGROUND AND AIMS IMPACT: is a disease-specific health-related quality-of-life questionnaire developed for use in pediatric inflammatory bowel disease through a process of patient interviews and analysis of patient responses to an item-reduction questionnaire. This study sought to assess the feasibility, reliability, and validity of the instrument. The readability statistics and number of unanswered questions were assessed among 147 patients (97 CD, 50 UC) with mean age 14.4 +/- 2.2 years (range 9.2-18.0 years) using the self-administered questionnaire. Internal consistency was assessed with Cronbach's alpha and test-retest reliability using intraclass correlation coefficient (ICC). Construct validity was based on a priori hypotheses. Mean total scores were compared by ANOVA among patients grouped according to disease activity and disease severity within the past year. The readability statistic showed a Flesch-Kincaid Grade level of 4.5. Only 0.68% of questions were left blank. Reliability was excellent with Cronbach's alpha = 0.96, and an ICC of 0.90 in patients with stable disease over a two-week period (n = 32). The mean total IMPACT score for patients with quiescent disease (180 +/- 32) was significantly higher (better QOL) than for those with active disease (146 +/- 31 for mild, 133 +/- 34 for moderate/severe) (P < 0.005). The IMPACT questionnaire is a valid and reliable reflection of health-related quality of life of older children and adolescents with both ulcerative colitis and Crohn's disease.