Transmission of rotavirus infection was studied in a birth cohort of children based in an urban slum in Vellore and their familial contacts. Contemporaneous samples from index patients and their familial contacts were collected for analysis in three different settings. Firstly, samples were collected from familial contacts during a period of rotavirus infection in children from the cohort. Secondly, on occasions when a family member had rotavirus diarrhea, samples from the cohort child were taken for analysis. Lastly, asymptomatic surveillance samples collected at predetermined time points from both the cohort child and familial contacts were analyzed. From 560 samples collected from family members during symptomatic and asymptomatic rotavirus infections in these children, three rotavirus transmissions were identified, accounting for a secondary attack rate of 0.54%. In four instances of rotavirus diarrhea in a family member, one infection was transmitted to the cohort child. Nucleotide sequence and phylogenetic analysis demonstrated a high degree of similarity in all these pairs ranging between 99% and 100% at both the nucleotide and the deduced amino acid levels, highly suggestive of person-to-person transmission of rotavirus infection. There was complete concordance of rotavirus genotyping between these pairs. No transmission events were noted from 14 asymptomatic rotavirus infections identified during routine surveillance of family members. This study is the first to use phylogenetic analysis to study the intrafamilial spread of rotavirus infection.