This cross-sectional and correlational study has estimated the quantitative relationship between placental weight and the concentration of lead in the placenta; has also estimated the association between placental weight with gestational age, weight, length and concentration of hemoglobin in newborns in a metallurgical region of Peru, when the Oroya smelter was working normally, because at present it has ceased its activity. Forty birth products, collected over a period of three months in II Hospital EsSalud La Oroya were valued. Biological sampling responded to preset protocols. Lead quantified by atomic absorption spectrometry with graphite furnace in the Peruvian Institute of Nuclear Energy. Bivariate regression analysis and Pearson linear correlation were performed to establish associations between assessed variables. The averages and standard deviation of gestational age, lead content in the placenta, placental weight; birth weight, length and hemoglobin level of neonates were 39.20±1.18 weeks, 319±215.86 ng/g, 504.25±83.53 g, 3191.75±310.61 g; 49.72±1.26 cm and 16.76±1.88 g/dL, respectively. The regression model best adapted to the assessed variables was the linear model. Higher levels of lead in the placenta were negatively correlated with the placental weight. The greatest placental weight was positively correlated to birth weight, length and hemoglobin concentrations of newborns.