ABSTRACT. The effect on breast feeding of various factors connected with delivery and the immediate post partum period were investigated in a group of 1701 parturients. Children born by caesarean section or assisted delivery, those of low birth weight or asphyxiated at birth started breast feeding significantly less often than healthy children delivered normally. The length of breast feeding was not affected by these factors once it was started, 49% breast feeding for six months or more. Exceptionally young and old mothers breast fed less well than mothers in general. Mothers whose husbands attended the delivery breast fed more often and longer than others. Failure to start breast feeding occurred in only 2.4% of the material. In this material with high breast feeding rates it can be concluded that obstetric and perinatal abnormalities have a small but nevertheless significant effect on the incidence of breast feeding.