The interpretation of variations in perinatal morbidity by immigration status has been difficult. Of particular concern is the lack of attention to adaptive capacity. This study explores the effect of acculturation on term low birthweight (LBW) in five ethnic groups representing different immigration experiences. Using Quebec birth certificates (1979-1988), two birth cohorts were defined to control for the effects of repeat pregnancies. Bivariate and logistic regression analyses were used to examine the relationship between acculturation and term LBW. In both birth cohorts the more acculturated women experienced significantly higher rates of term LBW. The odds ratio for term LBW (1.6) was also significantly higher for the more acculturated group but this effect was only observed in the second birth cohort. These findings imply that in addition to other conventional factors, the level of acculturation of the mother should be assessed in perinatal risk identification systems.