Introduction: Asthma is associated with increased airway responsiveness (AR) but the age when this relationship becomes established is not clear. The present study tested the hypothesis that the association between increased AR and asthma is established after one month of age. Methods: As part of a birth cohort study, AR was determined at ages one (early infancy), six (mid infancy) and twelve months (late infancy). At eleven years of age (childhood), AR and the presence of asthma symptoms were determined. Results: Of the 253 study subjects enrolled, AR was determined in 202 in early infancy, 174 in mid infancy, 147 in late infancy and 176 in childhood. Increased AR in late infancy, but not early or mid infancy, was associated with increased wheeze at age 11 years (p=0.016). Increased AR in infancy persisted into childhood in association with male gender, early respiratory illness and maternal smoking and asthma. Among those 116 assessed in both late infancy and childhood, recent wheeze was present in 35% of children with increased AR at both ages, 13% with increased AR in childhood only, 12% for those with increased AR in late infancy only and 0% for those who did not have increased AR at either age, p=0.005; the proportions of children with diagnosed asthma in the corresponding groups were 27%, 20%, 12% and 0%, p=0.037. Conclusions: The association between increased infantile AR and childhood asthma emerges at the end of the first year of life.