Background: With dramatic increase in incidence, life-long and remmiting course, debilitating symptoms, increased risk of surgery and treatment complications, Inflammatory bowel diseases (IBD) pose a growing medical and epidemiological problem. Health-related quality of life (HRQOL) has emerged as informative mean of assessing the impact of the disease burden on health as well ass determining the efficacy of medical care. ----- Objectives: To assess the reliability and validity of culturally adapted pediatric disease-specific HRQOL instruments, to compare HRQOL results of children suffering from IBD with results of healthy peers, to investigate accordance of selfreport and proxy reports, to disclose disease-specific variables which greatly influence patients' HRQOL and to report the prognostic validity of disease-specific HRQOL questionnaires. ----- Materials and methods: In a multicentric study, 104 children with IBD and 89 parents participated. HRQOL was assessed by generic (PedsQL™) and diseasespecific (IMPACT-III (HR) and SHS) questionnaires that were previously crosculturally adapted for use in Croatia. Factor analysis was used to determine optimal domain structure of IMPACT-III (HR), analysis of Crombac's alpha coefficients to test internal reliability, ANOVA and Kruskal-Wallis to assess dicriminant validity, correlation with PedsQL™ using Pearson coefficients to assess concurent validity. MCID sores were calculated for each IMPACT-III (HR) scale using the standard error of means. Accordance of self-reports and proxy reports was analysed by interclass correlation coefficients. Binary logistic models were inmplemented for the prognostic validty analysis. ----- Results: Cronbach’s alpha for the IMPACT-III (HR) total score was 0.92. The most robust factor solution was a 5-domain structure: Symptoms, Concerns, Socializing, Body Image, and Worry about Stool, all of which demonstrated good internal reliability (α=0.60-0.89), but two items were dropped to achieve this. Discriminant validity was demonstrated by significant differences (P < 0.001) in mean IMPACT-III (HR) scores between quiescent and mild or moderate-severe disease activity groups for total (148 vs. 139 or 125) and following factor scores: Symptoms (84 vs. 71 or 61), Socializing (91 vs. 83 or 76), and Worry about Stool (significant only between quiescent and moderate-severe groups, 90 vs. 62, respectively). For SHS, significant difference in domain scores beetween disease activity groups was confirmed for Symptoms (P=0.022) and Functinonig (P=0.003). Concurrent validity of IMPACT-III (HR) or SHS showed significant correlation, which was strongest when similar domains were compared. Responsivennes to change was showed for following SHS scales: Symptoms (P=0.032), Functioning (P=0.008), and Worries (P=0.021). Standard errors of measurement, which represent the MCID for each scale, were ranging between 4.9-11.4. Patients in remission had comparable HRQOL scores to healthy peers, with significantly higher scores in emotional functioning (P<0.01). When conpared to healthy peers, patients with active disease had significantly worse PedsQL™ scores for Physical Health (P<0.05), Social (P<0.05), and School Functioning (P<0.0001). In comparison of self and proxy reports, accordance was moderate to good (ICC=0.581-0.779). Mean total IMPACT-III (HR) scores significantly differed between Crohn's disease and ulcerative colitis (P=0.019). Hospitalisations for relapse, previous use of corticosteroids or azathioprine were were correlated with significantly lower HRQOL scores,P<0.001, P=0.047, P=0.008, respectively. Drop in HRQOL results of Worry About Stool domain of IMPACT-III (HR) predicted escalation of medicamentous therapy in next 6-12 months (OR=5.3; 95% CI=1.2-24.2). ----- Conclusion: IMPACT-III (HR) and SHS appear to be useful tool to measure health-related quality of life in Croatian children with Crohn’s disease and ulcerative colitis. It seems that induction and maintaince of remission in patients with IBD may provide HRQOL comparable to the healthy peers.