ABSTRACTObjectives:The aim of the present study was to better understand the exocrine pancreatic function of extremely preterm infants.Methods:Pancreatic‐specific elastase 1 (PSE1) activity was determined in spot stool samples of 69 preterm infants of gestational age <32 weeks and birth weight <1250 g. Assays were conducted on samples collected at 2 (N = 56), 4 (N = 46), and 6 weeks of age (N = 23).Results:PSE1 activity increased from week 2 (median [interquartile range] 84 [48–187] μg/g) to week 4 (164 [87–251 μg/g; P < 0.001) but not thereafter (169 [82–298] μg/g at week 6). The maturational increase in PSE1 activity was observed only in infants of gestational age <28 weeks (P < 0.001). At 2 weeks after birth, PSE1 levels were lower in infants of gestational age <28 weeks than in infants of gestational age ≥28 weeks (77 [43–110] vs 165 [56–300] μg/g; P = 0.019), but this difference was less pronounced at 4 weeks (153 [77–226] vs 230 [108–503] μg/g; P = 0.070) and had disappeared by 6 weeks (163 [76–258] vs 175 [85–418] μg/g; P = 0.576). In infants on full enteral feeding regimens 4 weeks after birth, PSE1 levels were associated with weight gain per unit of energy intake (Rs = 0.431; P = 0.005). This measure of weight gain was lower (P = 0.040) in infants with PSE1 levels <200 μg/g (0.110 [0.081–0.139] g/kcal, N = 25) than in those with PSE1 levels ≥200 μg/g (0.139 [0.117–0.157] g/kcal, N = 15). Administration of pancreatic enzymes to infants showing PSE1 excretion levels <200 μg/g did not enhance weight gain.Conclusions:Extremely preterm infants have limited exocrine pancreatic function during the first weeks of life, which may contribute to growth failure.