Objective To evaluate outcome data in an observational cohort of very low birth weight infants of the German Neonatal Network stratified to prophylactic use of Lactobacillus acidophilus / Bifidobacterium infantis probiotics. Study design Within the observational period (September 1, 2010, until December 31, 2012, n = 5351 infants) study centers were categorized into 3 groups based on their choice of Lactobacillus acidophilus / Bifidobacterium infantis use: (1) no prophylactic use (12 centers); (2 a/b) change of strategy nonuser to user during observational period (13 centers); and (3) use before start of observation (21 centers). Primary outcome data of all eligible infants were determined according to center-specific strategy. Results The use of probiotics was associated with a reduced risk for necrotizing enterocolitis surgery (group 1 vs group 3: 4.2 vs 2.6%, P  = .028; change of strategy: 6.2 vs 4.0%, P  < .001), any abdominal surgery, and hospital mortality. Infants treated with probiotics had improved weight gain/day, and probiotics had no effect on the risk of blood-culture confirmed sepsis. In a multivariable logistic regression analysis, probiotics were protective for necrotizing enterocolitis surgery (OR 0.58, 95% CI 0.37-0.91; P  = .017), any abdominal surgery (OR 0.7, 95% CI 0.51-0.95; P  = .02), and the combined outcome abdominal surgery and/or death (OR 0.43; 95% CI 0.33-0.56; P  < .001). Conclusions Our observational data support the use of Lactobacillus acidophilus / Bifidobacterium infantis probiotics to reduce the risk for gastrointestinal morbidity but not sepsis in very low birth weight infants.