Objectives: To examine the correlation between disease distribution, severity of symptoms and the existence of EIM. To examine the relationship between the length of symptoms before diagnosis and the response to initial therapy. Additionally, to explore differences in therapy response between IBD types and the role of gender and age in symptom severity and developmental delay. Study Design: A cohort study Participants and methods: The participants are pediatric IBD patients, with data sourced from Croatia's National Register of Children with Chronic Inflammatory Bowel Diseases. Results: Patients with more than one localization of inflammation in Crohn's disease had a more severe clinical presentation (P = 0,023). In Crohn's disease (CD), patients with a severe clinical presentation also had more EIM (P = 0,032). Most EIMs were prevalent in patients who had the colonic form of Crohn's disease; in 6 (25 %) patients. Children with Crohn's disease who received early therapy were more likely to respond to it (P = 0,05). Girls had more severe PCDAI score (P = 0,005), especially as they aged (P < 0,001). In ulcerative colitis, girls had significantly higher PUCAI scores than boys of the same age (P < 0,001). Among children with Crohn's disease under 12 years, boys grew better than girls (P < 0,001) and also thrive better than older boys (P = 0,002), while the opposite was found for girls (P = 0,005). In ulcerative colitis, there was no significant gender difference in growth, but younger boys had more normal BMI values (P = 0,045). Conclusion: In CD, tracking the location of inflammation is essential to assess disease progression and prevent complications. Timely diagnosis in CD enhances treatment effectiveness. Female patients with IBD should be monitored more frequently, as they tend to exhibit a more severe clinical presentation and are at a higher risk of developmental regression. It is important to keep an eye on the growth of older boys with CD in comparison to their healthy counterparts. Although there are no major gender differences in Ulcerative Colitis, measures should still be taken to prevent growth impairment.