Vitamin D deficiency is prevalent in chronic pancreatitis (CP), but the optimal route and dose of vitamin D supplementation are unknown. We evaluated the relative efficacy of two different doses of intramuscular (i.m.) vitamin D(3) in patients with CP and vitamin D insufficiency. In a double-blind randomized study, 40 patients with tropical calcific pancreatitis with serum 25-hydroxyvitamin D (25OHD) <75 nmol/L (mean 27.0 ± 14.5 nmol/L, <50 nmol/L in 90 %) were divided into three groups. Groups 1 and 2 received 600,000 IU (15,000 μg) and 300,000 IU (7,500 μg) i.m. cholecalciferol, respectively, while group 3 received i.m. saline. All groups received 1 g calcium and 500 IU (12.5 μg) vitamin D(3) orally daily and were studied for 9 months. The primary outcome was the proportion of patients with vitamin D sufficiency (25OHD >75 nmol/L) at 6 months. Vitamin D sufficiency was significantly different in the three groups (85, 29, and 0 % in groups 1, 2, and 3, respectively; p < 0.001). Mean 25OHD remained >75 nmol/L in months 1-6 in group 1 but reached a lower level (50-75 nmol/L) at these time points in group 2. At 6 months, serum alkaline phosphatase decreased significantly only in group 1 (230 ± 73 vs 165 ± 39 IU/L, p = 0.004). No patient in any group developed hypervitaminosis D or hypercalcemia. In conclusion, in patients with CP, a single i.m. injection of 600,000 IU was more effective at achieving vitamin D sufficiency over 6 months compared with 300,000 IU vitamin D(3). (Clinical Trials.gov number NCT00956839).