Introduction: Low Birth Weight (LBW) has multiple causes and continues to be a problem that affects different regions of Colombia. Objective: To determine factors associated with LBW in the Departmental University Hospital of Nariño (Colombia). Materials and methods: A case-control study that included newborns and mothers whose delivery took place between November 2014 and June 2015. Results: Risk of LBW was higher in: women aged between 10-19 years (OR=7.79, 95%CI=2.61-23.23); with history of vaginal infection during pregnancy (OR=4, 95%CI=1.26-12.66); and those affiliated with the subsidized health regimen (OR=4.96, 95%CI=1.71-14.41). The risk of having a newborn with LBW was reduced by 10% (OR=0.90, 95%CI=0.84-0.96) for each one unit increase in Body Mass index, and by 76% (OR=0.23, 95%CI=0.16-0.34) for each increase in one week of gestation. Conclusions: Most of the identified risk factors can be prevented or intervened with through an early public health approach.