OBJETIVO: Evaluar el efecto de la ganancia de peso gestacional (GPG) en la madre y el neonato. MATERIAL Y MÉTODOS: Se incluyeron 1 000 mujeres en puerperio inmediato atendidas en el Hospital de Ginecología del Instituto Mexicano del Seguro Social, en Tijuana, Baja California, México. Se consideró una GPG óptima si en las mujeres con bajo peso, peso normal, sobrepeso u obesidad previo al embarazo, la GPG fue OBJECTIVE: To evaluate the effects of gestational weight gain (GWG) on maternal and neonatal outcomes. MATERIALS AND METHODS: During 2009, women in the immediate puerperium were assessed at the Gynecology and Obstetrics Hospital in Tijuana, Baja California, Mexico. GWG was considered optimal when < 18 kg, < 16 kg, < 11.5 kg and <9 kg for women who, before pregnancy, were underweight, normal weight, overweight and obese, respectively. RESULTS: A total of 38% of women gained more than the recommended weight during pregnancy Women with normal weight previous to pregnancy who exceeded gestational weight-gain recommendations had a risk of oligo/polyhydramnios (OR 2.1, CI 95% 1.04-4.2) and cesarean delivery; overweight women previous to pregnancy had an increased risk of preeclampsia (OR 2.2 CI 95% I.I-4.6) and newborn macrosomia (OR 2.5, CI 95% 1.1-5.6); and obese women had a risk of newborn macrosomía (OR 6.6 IC 95% I.8-23). Pre-pregnancy weight was more greatly associated with gestational diabetes than gestational weight gain. CONCLUSIONS: Women whose weight gain during pregnancy is outside of the recommended ranges had an increased risk of adverse obstetric and neonatal outcomes.