Objective Although vitamin and mineral supplementation for nutritional deficiencies is a common component of pediatric inflammatory bowel disease (IBD) management, little is known about supplement adherence in this group. This study described adherence to multivitamin, iron, and calcium supplements among 49 youth aged 11–18 years with IBD. Additionally, the study examined relationships between supplement knowledge and adherence. Methods Participants completed supplement adherence ratings using a validated interview. Knowledge was assessed using an open-ended question from the same interview; responses were later categorized into 1 of 3 knowledge sophistication categories (low, moderate, or high). Results Mean adherence rates ranged from 32 to 44% across supplements. Youth who did not know the reason for supplementation (approximately 25% of the sample) displayed substantially poorer adherence than did those with moderate or high levels of knowledge, across all supplements. Conclusions Findings highlight the importance of evaluating and addressing nonadherence to vitamin and mineral supplements in youth with pediatric IBD.