ObjectivesTo determine time to diagnosis in a paediatric inflammatory bowel disease (IBD) cohort and the relative contribution of the component intervals, and to identify factors associated with diagnostic delay.DesignProspective cohort studySettingSingle-centre study including children with incident IBD at the Hospital for Sick Children diagnosed between December 2013 and December 2015.InterventionsTime to diagnosis and its subintervals were determined and patient, disease and institutional factors were tested for associations.ResultsAmong 111 children, the median overall time to diagnosis was 4.5 (IQR 2.1–8.8) months. Time to diagnosis was longer in Crohn’s disease (CD) than ulcerative colitis (UC) (median 6.8 (IQR 2.9–12.5) vs 2.4 (IQR 1.3–5.3) months) and patients with isolated small bowel disease. Twenty per cent of patients were diagnosed≥1 year after symptom onset (86% CD, 14% UC, p=0.003). Time from symptom onset to gastroenterology referral was the greatest contributor to overall time to diagnosis (median 2.9 (IQR 1.6–8.2) months). Height impairment was independently associated with diagnostic delay (OR 0.59, p=0.02, for height-for-age z-score (HAZ), signifying almost 70% increased odds of delay for every 1 SD decrease in HAZ). This height discrepancy persisted 1 year after diagnosis. Bloody diarrhoea was protective against delay (OR 0.28, p=0.02). The subinterval from referral to diagnosis was shorter in patients with laboratory abnormalities, particularly hypoalbuminaemia.ConclusionsDiagnostic delay was more common in CD and associated with height impairment that persisted 1 year after presentation. The greatest contributor to time to diagnosis was time from symptom onset to referral.