CONTEXT AND OBJECTIVE: Excessive gestational weight gain is related to many complications (both maternal and fetal), such as macrosomia. The most common complications in macrosomic fetuses include: increased risk of intrauterine death, need for intensive care, fractures, neonatal hyperbilirubinemia, paralysis of the brachial plexus and obesity in childhood and adulthood. The aim of this study was to evaluate the association between gestational and fetal weight gain and the incidence of macrosomia in two maternity hospitals. DESIGN AND SETTING: Cohort study in two public maternity hospitals in Goiânia, Brazil. METHODS: This was a cohort study on 200 healthy pregnant women with normal body mass index, divided into two groups: one with normal weight gain and the other with excessive weight gain during pregnancy. RESULTS: The cohorts were similar regarding maternal age, per capita income, schooling level and reproductive behavior. The fetal weight was greater in the cohort with excessive maternal weight gain (3,388.83 g ± 514.44 g) than in the cohort with normal weight (3,175.86 g ± 413.70 g) (P < 0.01). The general incidence of macrosomia was 6.5%: 13.0% (13 cases) in the cohort with excessive maternal weight gain and 0.0% (0 cases) in the cohort with adequate weight gain. CONCLUSION: Excessive maternal weight gain was associated with increased fetal birth weight and incidence of macrosomia.