BACKGROUND: Although long-chain omega-3 (n-3) PUFAs (LComega3PUFAs) have been linked to the prevention of some inflammatory disorders, little is known about the association between these fatty acids and incidence of asthma. OBJECTIVE: The objective was to prospectively investigate the association between LComega3PUFAs and fish intake and incidence of asthma among American young adults. DESIGN: A 20-y follow-up longitudinal analysis was conducted in a biracial cohort of 4162 Americans, aged 18-30 y, with a history of asthma at baseline in 1985. Diet was assessed by a validated interviewer-administered quantitative food-frequency questionnaire at the examinations in 1985, 1992, and 2005. Incident self-reported asthma was defined as having a physician diagnosis of asthma and/or the use of asthma medications between 1985 and 2005. RESULTS: During the 20-y follow-up, 446 incident cases of asthma were identified. LComega3PUFA intake was significantly inversely associated with incidence of asthma after adjustment for sociodemographic, major lifestyle, and dietary confounders. The multivariable-adjusted HR for the highest quintile of LComega3PUFA intake as compared with the lowest quintile was 0.46 (95% CI: 0.33, 0.64; P-trend < 0.01). However, a higher frequency of nonfried fish consumption was not significantly associated with the risk of asthma. DHA showed a greater inverse association than did EPA. The association between LComega3PUFAs and incident asthma was not appreciably modified by sex, race, BMI, smoking status, or atopic status. CONCLUSION: This study showed that intakes of LComega3PUFAs are inversely longitudinally associated with the incidence of asthma in American young adults.