Rationale: The proportion of low and very low birthweight births is increasing. Infants and children with a history of low and very low birthweight have an increased risk of respiratory illnesses but it is unknown if clinically significant disease persists into adulthood. Objective: To determine if a history of low birthweight is associated with hospitalization for respiratory illness in adulthood. Methods: A population-based case-control study: Cases were adults ages 18-27 hospitalized for a respiratory illness from 1998-2007 within Washington State who could be linked to a Washington State birth certificate for the years 1980-1988. Four controls, frequency matched by birth year, were randomly selected from Washington State birth certificates for each case patient. Controls that died prior to age 18 were excluded. Measurements: Two levels of exposure were identified: very low birthweight (birthweight <1500 grams) and moderately low birthweight (birthweight 1500-2499 grams). Normal birthweight individuals (2500-4000 grams) were considered unexposed. Respiratory hospitalizations were defined using discharge diagnosis codes. Logistic regression was used to calculate the odds ratio for hospitalization comparing exposed and unexposed individuals. Main Results: 4674 case patients and 18,445 controls were identified. The odds ratio for hospitalization for respiratory illness was 1.83 for very low birthweight (95% CI 1.28-2.62, p=0.001) and 1.34 for moderately low birthweight (95% CI 1.17-1.53, p<0.0005). This association remained after adjustment for birth year, sex, maternal age, race, residence and marital status. Conclusions: Adults with a history of very low birthweight or moderately low birthweight were at increased risk of hospitalization for respiratory illness.