BACKGROUND AND AIMS: Nationwide, population-based studies of chronic non-bacterial osteomyelitis (CNO) in patients with childhood-onset inflammatory bowel disease (IBD) are lacking. METHODS: We used nationwide registers to identify all children in Sweden diagnosed with IBD during 2002-2022 and the occurrence of CNO in this IBD cohort and general population non-IBD comparators. To estimate the temporal associations between IBD and CNO we used Cox regression. We compared clinical data for IBD patients with CNO (IBD+CNO) and the IBD patients without CNO. RESULTS: We identified 8244 children with IBD and 82 400 non-IBD comparators. At IBD diagnosis, CNO had been diagnosed in 0.13% (11/8244) of the IBD cohort and 0.03% (26/82 400) of the non-IBD comparators. During follow-up, 13 additional CNO cases occurred in the IBD cohort and 22 in the non-IBD comparators (adjusted hazard ratio = 5.87 [95% CI 2.95-11.66]). The prevalence of CNO among all prevalent children with IBD and prevalent matched non-IBD comparators December 31, 2022 was 0.48% (9/1885) and 0.02% (4/18 567), respectively. Median age at IBD diagnosis was lower in IBD + CNO compared to IBD without CNO (11 vs 14 years [-3 years, 95% CI -5 to -1]). Extraintestinal manifestations (except CNO) were more frequent in IBD + CNO (62% vs 21%, P < .0001). Treatment with biologics was more common in the IBD + CNO group (78% vs 44%, P = .004), prescribed for IBD and/or CNO. CONCLUSIONS: We found a 6-fold increased risk of CNO in childhood-onset IBD compared to non-IBD comparators. Patients with IBD + CNO are characterized by younger age at IBD onset, more frequent extraintestinal manifestations, and higher usage of biologics.