144 children with a known breast feeding history were studied for their caries prevalence and level of salivary mutans streptococci. 19% of the children were exclusively breast-fed for more than 9 months and 38% of the children were weaned after the age of 12 months (max. 34 months). The results of the study showed an equal caries prevalence at the age of 5 among children with a longer or shorter period of exclusive breast-feeding (chi 2 = 3.68, 9 df, NS). Exclusive breast-feeding also did not affect the levels of salivary mutans streptococci (chi 2 = 4.87, 9 df, NS). Children who were weaned late did not differ from those who were weaned early with respect to caries experience (chi 2 = 6.12, 9 df, NS), level of salivary mutans streptococci (chi 2 = 5.49, 9 df, NS) or presence of mutans streptococci (chi 2 = 1.53, 4 df, NS). On the basis of our sample we concluded that breast feeding alone cannot be connected with an increased or lowered caries prevalence.