The Institute of Medicine recommends that short women gain less weight during pregnancy than taller women in order to reduce the risk of high birthweight, which can lead to feto-pelvic disproportion. This recommendation, however, is based on clinical judgment rather than on epidemiologic evidence, as few studies have examined the relationships between maternal height, pregnancy weight gain, and infant birthweight. Our objective was to determine whether maternal height is an independent risk factor for infant birthweight and to assess whether maternal height modifies the effect of pregnancy weight gain on infant birthweight. We examined the relationship between maternal height and infant birthweight in a multi-ethnic cohort of 8,870 women with uncomplicated pregnancies who delivered singleton infants at the University of California, San Francisco, 1980-1990. Using multiple linear regression, we modeled the contribution of height and weight gain to birthweight in four different ethnic groups. Increasing maternal height was significantly and positively associated with infant birthweight in White, Black, and Asian women, but not Hispanic women. The relationship between pregnancy weight gain and infant birthweight was not modified by maternal height. Am. J. Hum. Biol. 12:682-687, 2000. Copyright 2000 Wiley-Liss, Inc.