Introduction: The birth weight is one of the most useful indicators to evaluate the perspectives of infantile survival and health during its first year of life. Objective: To estimate proportion of low birth weight (LBW) and the perinatal mortality rate (PMR) in a public institution of health of third level of complexity of Bucaramanga. Materials and methods: Retrospective and descriptive study. Data like gestational age, gender, weight, height, cephalic perimeter, childbirth type was taken. In the descriptive analysis, the quantitative variables were calculated the measures of central tendency and dispersion with intervals of trust of 95%; and for the qualitative variables the respective proportions were calculated. Results: Proportion of LBW was of 17.79% (IC 95%: 16.51%-19.13%). The perinatal mortality rate was 16.4 per 1000 live births and a high percentage (83%) of the passed away RN displayed BPN. The 77.8% of newborns with low birth weight, stunted presented asymmetrical and 22.1% growth retardation symmetrical. Conclusion: The high proportion of LBW found in this study is similar to that found in a university hospital in reference to high risk pregnancies (19.5%). Salud UIS 2008; 40: 185- 190