OBJECTIVE: To investigate the relation of infant feeding practice to childhood respiratory illness, growth, body composition, and blood pressure. DESIGN: Follow up study of a cohort of children (mean age 7.3 years) who had detailed infant feeding and demographic data collected prospectively during the first two years of life. SETTING: Dundee. SUBJECTS: 674 infants, of whom 545 (81%) were available for study. Data on respiratory illness were available for 545 children (mean age 7.3 (range 6.1-9.9) years); height for 410 children; weight and body mass index for 412 children; body composition for 405 children; blood pressure for 301 children (mean age 7.2 (range 6.9-10.0) years). MAIN OUTCOME MEASURES: Respiratory illness, weight, height, body mass index, percentage body fat, and blood pressure in relation to duration of breast feeding and timing of introduction of solids. RESULTS: After adjustment for the significant confounding variables the estimated probability of ever having respiratory illness in children who received breast milk exclusively for at least 15 weeks was consistently lower (17.0% (95% confidence interval 15.9% to 18.1%) for exclusive breast feeding, 31.0% (26.8% to 35.2%) for partial breast feeding, and 32.2% (30.7% to 33.7%) for bottle feeding. Solid feeding before 15 weeks was associated with an increased probability of wheeze during childhood (21.0% (19.9% to 22.1%) v 9.7% (8.6% to 10.8%)). It was also associated with increased percentage body fat and weight in childhood (mean body fat 18.5% (18.2% to 18.8%) v 16.5% (16.0% to 17.0%); weight standard deviation score 0.02 (-0.02 to 0.06) v -0.09 (-0.16 to 0.02). Systolic blood pressure was raised significantly in children who were exclusively bottle fed compared with children who received breast milk (mean 94.2 (93.5 to 94.9) mm Hg v 90.7 (89.9 to 91.7) mm Hg). CONCLUSIONS: The probability of respiratory illness occurring at any time during childhood is significantly reduced if the child is fed exclusively breast milk for 15 weeks and no solid foods are introduced during this time. Breast feeding and the late introduction of solids may have a beneficial effect on childhood health and subsequent adult disease.