Ethnicity differences account for genetic, environmental, lifestyle, and reproductive variables, influencing the rate of twinning (Nylander, 1981). Frequently, ethnic differences correlate with variable perinatal care leading to differences in outcome. Free access to antenatal care, and to facilities for delivery and neonatal care is available for the entire population in Israel, and therefor differences attributed to levels of medical care are practically negligible. We previously evaluated the overall relationship between ethnicity and outcome in a popula-tion-based cohort of mothers of twins (Goldman et al., 2001). However, the overall comparison may have masked some differences that could be present. The purpose of this study was to evaluate whether ethnicity is associated with differences in perinatal outcome in randomly selected, matched-controlled Israeli Jewish and Muslim mothers of twins.