It has been suggested that consumption of fish and polyunsaturated fatty acids could have a protective effect against inflammation in the airways and the development of asthma and other allergic diseases. Our objective was to test the hypothesis that fish consumption during the first year of life decreases the risk of childhood asthma and allergic rhinitis. We assessed the relation between introduction of fish in the diet during the first year of life and risk of asthma and allergic rhinitis in a prospective 4-year cohort study of 2531 Norwegian children. We estimated odds ratios (OR) in logistic regression analysis adjusting for potential confounders. A total of 47.6% children had fish during the first year of life. The adjusted OR for allergic rhinitis was 0.45 (95% confidence interval [CI]=0.28, 0.74) and for asthma 0.84 (95% CI=0.57, 1.22). Fish consumption in the first year of life may reduce the risk of developing asthma and allergic rhinitis in childhood.