Upon examining the records of the Hospital "B" of the Department of Health, which gives service to the rural area of the Mezquital valley, inhabited largely by an Otomi speaking population, this study found that the average weight of newborn infants was 2946 gr in males and 2859 gr in females Based on the total number of births at the hospital, during 1975-1978, 8% were premature and 13% of the infants were born at full term but weighed less than 2500 gr. It is probable that the causes of low birth weight and premature births may be due to the poor socioeconomic conditions of the area and the lack of medical attention during pregnancy.En esta investigación se analizan algunos factores que intervienen en el peso de un recién nacido prematuro, los expedientes se obtuvieron de un hospital popular del municipio de Ixmiquilpan, Hidalgo, los resultados muestran que la causa principal de este fenómeno son los bajos recursos económicos y la mala nutrición en la vida adolescente de las mamás que procrean en edades jóvenes a estos niños.