The records of Caucasoid (589) and Negroid (142) mothers of twins, and of a control soup of mothers of singletons (1267 Caucasoids and 248 Negroids) born from 1984 to 1993 in the largest maternity hospital of Campinas, SP, Brazil (Maternidade de Campinas) were investigated for the following traits: type of hospital care, marital status, maternal age, occurrence of labor, type of delivery, parity, previous spontaneous abortions, gestational age, birth weight and birth length of twins and singletons. The main conclusions were: 1) the proportion of women whose hospital and medical care expenses were covered by welfare program or who were indigent was significantly higher among Negroids than among Caucasoids, but twinning was not associated with social class; 2) the proportion of married women among Caucasoids was higher than among Negroids, and a greater proportion of Caucasoid mothers of twin births were married as compared to mothers of singletons; 3) Caucasoids and Negroids did not differ concerning mean maternal age, occurrence of labor, type of delivery, rate of previous spontaneous abortions, and mean gestational age; 4) when compared to women who bore singletons, mothers of twin births were, on the average, almost two years older, and had a lower proportion of labor, a higher proportion of cesarean sections, and a higher abortion rate, while the twins had a lower mean gestational age (three weeks) than singletons; 5) parity among Caucasoids was lower than among Negroids, and in both races mothers of twin births had a higher parity than mothers of singletons; 6) twins had a lower mean weight and height at birth than singletons, males were slightly heavier than females, and Negroids were slightly lighter at birth than Caucasoids.202311318