BACKGROUND & AIMS: Vitamin D at serum 25(OH)D concentrations above 100 nmol/L is associated with disease remission in patients with IBD, suggesting targeted dosing might be anti-inflammatory. This study aimed to assess the effectiveness, safety and predictors of a 12-week regimen of vitamin D supplementation to achieve such a target in patients with active disease. METHODS: In a pilot study, patients with active colitis and a serum 25(OH)D concentration <75 nmol/L were prescribed oral liquid vitamin D supplementation over 12 weeks using a specific protocol with dose adjusted 4-weekly to aim for a target level of 100-125 nmol/L. RESULTS: Five patients each with Crohn's colitis or ulcerative colitis (UC) had mean 25(OH)D concentration 52 (range 27-73 nmol/L). Five reached the targeted level and four 89-95 nmol/L. One withdrew after 4 weeks (88 nmol/L). Target dose was met only in those with BMI <30 kg/m2 and total dose inversely correlated with initial serum 25(OH)D. One patient had developed a high level at 8 weeks (146 nmol/L) and another new hypercalciuria. There were no serious adverse events attributable to the therapy. Clinical disease activity consistently declined, but faecal calprotectin and circulating markers of inflammation did not. CONCLUSIONS: A specified oral vitamin D regimen successfully and safely achieved target or near-target levels, improved symptom-based activity scores, but did not alter objective measures of intestinal or systemic inflammation. A modified version of this dose-escalating regimen would be suitable for a randomised placebo-controlled trial, but does require regular safety monitoring. Copyright © 2017 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.