Background: Pediatric inflammatory bowel disease (IBD) presents with extensive phenotype. The aim of this study was to determine the phenotype of pediatric IBD patients in Croatia at diagnosis and follow-up. Methods: Children were prospectively recruited into Croatian IBD national registry. Data on diagnostic evaluation, therapy and 1-year follow-up were collected. Results: A total of 51 newly diagnosed patients were recruited (19 Crohn's disease (CD), 28 ulcerative colitis (UC) and 4 IBD-unclassified (IBD-U)). Most common location in CD was ileocolonic disease (52.6%), and pancolitis in UC (53.6%). The recommended complete diagnostic algorithm was performed only in 29.4% of patients. First-line therapy used in CD was exclusive enteral nutrition for remission induction (84.2%) and azathioprine for maintenance (73.7%). In patients with UC, aminosalicylates were the most common drug used (89.3%). By the end of the first year 41.2% of CD and 53.9% of UC patients had one or more relapses and required treatment escalation. Conclusion: Our data confirm extensive intestinal involvement in pediatric IBD and relatively high relapse rate during the first year of follow-up. More effort should be invested on the national level to implement more stringent adherence to the current European guidelines. Impact: The key message of our article is that pediatric IBD in Croatia shows extensive intestinal involvement with high relapse rates in first year of follow-up. It is the first cohort study reporting on the phenotype of pediatric IBD in Croatia, but also investigates adherence to diagnostic and therapeutic European guidelines which is not commonly reported. The study is national based, thus having the greatest impact on Croatian health care,stressing out that more effort should be invested on the national level to implement more stringent adherence to the current European guidelines.