Analyses were made on birth weight of 2706 kids (six genetic groups) under confinement conditions in the arid zone of northern Mexico, to study the effect of air temperature (mean annual temperature = 21·1 °C) during gestation on this trait. The relationship of environmental temperature at kidding and survival of kids was also studied. Birth weight was significantly negatively related to mean dry bulb air temperature during gestation (reduction of 40±3 g for 1 °C increase in mean air temperature during gestation; r = −0·22; P < 0·01), although temperature only explained 5% of the variance of kid birth weight. Mean minimum temperatures (< 4 °C) 5 days after birth significantly reduced kid survival (83% v. 89–93% for kids born when temperatures were above 4 °C; P < 0·01). Air temperatures between 30 and 41 °C during the perinatal period did not affect (P > 0·05) survival rate. These results suggest that newborn kids seem to be relatively resistant to high air temperature, but are fairly susceptible to cold stress. Also, birth weight of kids from goats exposed to high air temperature during pregnancy was marginally reduced, although this was of limited economic significance.