To compare rates of necrotising enterocolitis (NEC), late-onset sepsis, and mortality in 5-year epochs before and after implementation of routine daily multistrain probiotics administration in high-risk neonates. Single-centre retrospective observational study over the 10-year period from 1 January 2008 to 31 December 2017. Level 3 neonatal intensive care unit (NICU) of the Norfolk and Norwich University Hospital, UK. Preterm neonates at high risk of NEC: admitted to NICU within 3 days of birth at <32 weeks' gestation or at 32-36 weeks' gestation and of birth weight <1500 g. Prior to 1 January 2013 probiotics were not used. Thereafter, dual-species and combination probiotics were routinely administered daily to high-risk neonates; from April 2016 triple-species probiotics ( and subspecies ) were used. Incidence of NEC (modified Bell's stage 2a or greater), late-onset sepsis, and mortality. Rates of NEC fell from 7.5% (35/469 neonates) in the pre-implementation epoch to 3.1% (16/513 neonates) in the routine probiotics epoch (adjusted sub-hazard ratio=0.44, 95% CI 0.23 to 0.85, p=0.014). The more than halving of NEC rates after probiotics introduction was independent of any measured covariates, including breast milk feeding rates. Cases of late-onset sepsis fell from 106/469 (22.6%) to 59/513 (11.5%) (p<0.0001), and there was no episode of sepsis due to or . All-cause mortality also fell in the routine probiotics epoch, from 67/469 (14.3%) to 47/513 (9.2%), although this was not statistically significant after multivariable adjustment (adjusted sub-hazard ratio=0.74, 95% CI 0.49 to 1.12, p=0.155). Administration of multispecies and probiotics has been associated with a significantly decreased risk of NEC and late-onset sepsis in our neonatal unit, and no safety issues. Our data are consistent with routine use of and combination probiotics having a beneficial effect on NEC prevention in very preterm neonates.