Postnatal cytomegalovirus (HCMV) infection is well characterized in preterm infants, where it can lead to severe symptomatic infection. We analyzed the rate and route of transmission of postnatal HCMV infections in full-term babies during the first year of life. A cohort of 120 HCMV seropositive mothers and their 122 newborns were tested after delivery for HCMV DNA shedding in different bodily fluids. Postnatal HCMV infection was defined as the detection of >2.5×10 ² HCMV-DNA copies/mL in infants’ saliva swabs. Maternal neutralizing antibody serum titer, HCMV specific T-cell response, and HCMV glycoprotein B (gB) IgG on breastmilk were analyzed. HCMV shedding was detected in 67 of 120 mothers (55.8%), and 20 of 122 infants (16.4%) developed HCMV infection within the first three months of life. Six additional infants were infected during the first year, for a postnatal infection rate of 21.3%. Viral shedding was more frequent in breastmilk than saliva, urine and vaginal secretions, and the mothers of infected infants showed higher levels of HCMV-DNA in milk. No association was found between the antibody levels in serum or milk and maternal viral shedding, whereas a slightly lower frequency of HCMV-specific CD4 ⁺ T-cells with long-term memory phenotype was observed in women with HCM-DNA-positive milk. About one out of five infants develop HCMV infection within the first year of life. Breastmilk appears the major route of transmission of the infection, maternal saliva have a minor role whereas the role of vaginal secretions is negligible.