The role of early probiotic supplementation in infants for the prevention of respiratory viral illnesses is unclear. We examined the association of Lactobacillus rhamnosus GG (LGG) supplementation during the first 6 months of life with the frequency and severity of viral illnesses during the first 24 months of life. We conducted a secondary analysis of data from the randomized controlled Trial of Infant Probiotic Supplementation (n = 184). Parents reported the number of respiratory viral illnesses, and a composite severity score was created based on symptoms. A negative binomial regression model and a mixed-effects linear regression model assessed for differences in the number of episodes and severity of episodes between treatment groups, respectively. There was no significant difference in the incidence rate of viral illness episodes or symptom severity between treatment groups. Daily supplementation with LGG in early infancy does not decrease the number or severity of viral illnesses during the first 2 years of life.