Background: Early childhood caries has been characterized as first affecting the primary maxillary anterior teeth, followed by the involvement of the primary molars. Other terms for dental caries in preschool children, which inappropriately may imply cause for the disease, includes baby bottle tooth decay, nursing caries, milk bottle syndrome, baby bottle caries, nursing bottle mouth and nursing mouth. Aim: To explore the relationships of feeding practices, age and number of teeth present with mutans streptococci colonization in infants. Design and setting: A comparative clinical study conducted on 160 children aged from 6 to 30 months in the Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital in collaboration with Child Health Institute and Research Center and Department of Oral Pathology and Microbiology, Bapuji Dental College and Hospital, Davangere. Materials and methods: Baseline data collection included: (i) Parents of the infants were asked open ended questions about the baby feeding practices, (ii) The age of the subjects were obtained from the immunization register maintained at Child Health Institute and Research Center and were grouped into group I (6-11 months), group II (12-17 months), group III (18-23 months) and group IV (24-30 months), (iii) Clinical examination of children was done by using mouth mirror and explorer in flash light.⁶ For each child number and location of erupted teeth was recorded, (iv) Microbial screening for mutans streptococci involved sampling of saliva from each child was performed by placing a sterile wooden tongue blade on the dorsum of the tongue and the number of colony forming units (CFU) were recorded. Results: According to feeding practices, 34 children were in breastfed category, 39 were in baby bottle category and 87 children reported no bottle usage. Out of 160 children examined, a total 142 children were colonized with mutans streptococci. 18 children were found to be colonized with low colony forming units, 78 children were found to be colonized with moderate colony forming units and 64 children were colonized with high colony forming units. In baby bottle group, all of 39 subjects were reported to have sweetened milk, sugar in the bottle. Conclusion: Among different feeding practices, all the three subgroups viz breastfed children, children with nursing bottle usage and children with no bottle usage, all have shown mutans streptococci acquisition. But breastfed children have shown least number of high colony forming units, which is increased in the case of children using nursing bottle and is maximum in the children who were neither breastfed nor fed with nursing bottle. Percentage of children colonized with mutans streptococci increases with age and as the number of teeth increase, number of colony forming units were also found to be increasing.