OBJECTIVES: Physical activity in paediatric and young adult patients suffering from inflammatory bowel disease (IBD) may play an important role in the overall health status. However, physical activity in these patients has not been reported using objective methods. We aimed to describe accelerometry-measured physical activity levels in paediatric and young adult IBD patients with either ulcerative colitis (UC) or Crohn's disease (CD). METHODS: We recruited Danish patients with IBD aged 10-20 years in clinical remission and with a faecal calprotectin below 200 µg/mg. Physical activity was assessed using tri-axial wrist accelerometry over seven days and quantified using the activity-related acceleration derived as the conventional Euclidian Norm Minus One (ENMO) metric expressed in milli-gravity units (mg). Time spent in Moderate-to-Vigorous Physical Activity (MVPA) was classified as ENMO > 210 mg in 5 s epoch resolution (unbouted). RESULTS: We included 61 patients with a median age of 17 years [Inter Quartile Range, IQR 14-19]. The total volume of activity expressed as average acceleration (ENMO) per day was 31.5 mg (95% CI 29.1-33.9). Time spent in unbouted MVPA was 32 min per day (95% CI 26-37). There was no significant difference in activity volume between patients with UC to patients with CD, the adjusted linear regression coefficient was - 1.7 mg (95% CI -6.2-2.7). Activity volume was higher for males (36.2 mg, 95% CI 31.9-40.5) than for females (27.8 mg, 95% CI 25.6-30.0), and younger patients were more active than older patients; Activity volume in 10-13 year olds was 37.2 mg (95% CI 28.6-45.7), whereas it was 28.5 mg (95% CI 25.2-31.7) for those aged 18-20 years. CONCLUSIONS: We collected tri-axial accelerometry in young patients with IBD in clinical remission, and described their level of physical activity by the conventional ENMO measure. We found no statistically significant difference in patients with UC compared to patients with CD. The volume of physical activity was higher in males compared to females, and inversely associated with age.