Objectives. We tested the hypothesis that 25-hydroxyvitamin D3 (25OHD) changes during acute inflammation in humans. Methods. Patients with first episode of acute pancreatitis were included. Blood samples were acquired on admission and on days 1, 2, and 14. Results. In total, 73 patients (35 males, median age 59) entered the study. On admission, the distribution of 25-OHD levels was as follows: severely deficient (<13 nmol/L) 23%; deficient (13–25 nmol/L) 20%; insufficient (26–50 nmol/L) 40%; and normal (<50 nmol/L) 17%. There was a significant fall and linear trend in 25OHD, albumin, and hemoglobin from day 0 to day 2. From day 0 to day 2 the drop in 25OHD was 3.1 nmol/L (95% CI 0.59–5.63). The changes from day 0 to day 2 in 25OHD were associated with changes in C-reactive protein (p = 0.02) but not with leukocyte or monocyte count. Conclusions. The 25OHD levels dropped during the first 2 days of acute pancreatitis beyond what was expected based on 25OHD half-life. This study supports our hypothesis that an acute inflammatory condition utilizes 25OHD, but other mechanisms could interfere.