Epidemiological studies of respiratory illness in childhood have used the mother's recall of her child's respiratory illness experience as a measure of the frequency with which these illnesses occur. This paper explores the relationship between the diagnosis by the doctor of lower respiratory illnesses and the recall by the mother of the occurrence of these illnesses in a cohort of children in the first year of life. While there is a poor relationship between doctor diagnosis and maternal recall of these illnesses, the group of children reported by their mothers to have had bronchitis or pneumonia in the first year of life appear to suffer more respiratory illness than those children whose mothers recall no such illnesses.