Dental caries was investigated in 248 4-year-old children in the Lohja District Health Centre, Finland in relation to the postpartum caries incidence rate in their mothers and the frequency of salivary close contacts between mothers and babies when the latter were 7 months old. Dental caries occurred in 32% of the children. Frequent maternal consumption of sugar-containing foods and drinks was significantly associated with a high maternal caries incidence rate. The mothers who had frequent close contacts with their babies gave them significantly more sweet comforters than the mothers who did not have close contacts frequently. However, only 25% of the children (n = 44) who had frequent maternal close contacts and whose mothers had a high caries incidence rate had caries, although levels of risk factors (bottle feeding with juices, frequent consumption of refined foodstuffs, added sugar and sweets, infrequent toothbrushing) were highest for these children. Dental caries was significantly more frequent in children in whom maternal caries incidence was low and close contacts were frequent (n = 35, 40%) and in those in whom maternal caries incidence was high and close contacts were rare (n = 55, 45%) than in those in whom maternal caries incidence was low and close contacts rare (n = 68, 18%). The results of the study support the theory that maternal caries incidence and salivary contacts with a child are connected with caries infection and immunity. Variations in bacterial challenge via such factors before and during the eruption of teeth may modify caries development in the primary dentition.