RATIONALE: Laboratory and clinical evidence suggests synergy between rhinoviruses and Streptococcus pneumoniae in the pathogenesis of respiratory tract infections. However, it is unclear whether rhinoviruses promote pneumococcal acquisition and transmission. OBJECTIVES: To describe the impact of rhinovirus infection on the acquisition and transmission of pneumococci within families with children. METHODS: We investigated 29 families with at least two children. The follow-up started at the onset of respiratory infectious symptoms in any family member and consisted of daily symptom diary and nasal swab samples from each participant twice per week for 3 weeks. Swabs were taken by the parents and sent to a study clinic by mail. Rhinoviruses were detected by reverse transcription-polymerase chain reaction and typed by sequencing. Pneumococci were identified by an antigen test and by standard culture methods, serotyping, and whole-genome sequencing. The effect of rhinovirus infection on the rates of pneumococcal acquisition and within-family transmission was estimated from the observed acquisition events and person-times spent uncolonized, using Poisson regression. MEASUREMENTS AND MAIN RESULTS: Rhinovirus was detected in 38 subjects (30%) at the onset and in 86 subjects (67%) during the follow-up. S. pneumoniae was detected on the first day in 9 (7%) and during follow-up in 38 (30%) subjects. Children with rhinovirus infection had a 4.3-fold rate of pneumococcal acquisition from the community (95% confidence interval, 1.1-15.4) and a 14.8-fold rate of within-family transmission (95% confidence interval, 3.1-69.6) compared with children without rhinovirus infection. CONCLUSIONS: Rhinovirus infection within families facilitates acquisition and within-family transmission of S. pneumoniae.