OBJECTIVE The purpose of the study was to assess mutans streptococci (MS) count in children who were treated for early childhood caries (ECC) in a follow-up examination. METHODS Forty-four children who were treated for ECC in the pediatric dentistry clinic of the Hebrew University-Hadassah School of Dental Medicine were given paraffin film to chew. A blade containing children's saliva was placed inside a test tube containing MS selective medium to allow bacteria growth. The kits were transferred immediately to the laboratory and incubated for 48 hours in a 37 degrees C incubator. After incubation, bacterial growth was counted by the amount of colonies formed. RESULTS Children who were examined closer to the end of the dental treatment demonstrated significantly lower MS counts. In addition, children who had higher birth weight also demonstrated lower bacterial counts. Significantly more parents of children with the high MS group than in the low MS group count reported that oral hygiene instructions greatly reduced children's plaque levels. All the children who were born preterm had high MS count, while 77% of children who were born at term demonstrated high MS count. CONCLUSIONS Children who had dental treatment due to ECC may have high MS count in the future and are at risk for caries attack. Factors that may be associated with high MS counts are low birth weight and mother's education.