Inadequate immunization has been a major cause of epidemic measles, but risk factors for inadequate immunization are poorly characterized. By using measles data bases and computerized birth certificate files, we identified a retrospective cohort of 1,070 Texas-born children who were aged 15 months to 10 years when they had measles during the 1988 to 1991 epidemics. We used measles and birth certificate data, including prenatal care and demographic information, to determine immunization status and risk factors for inadequate measles immunization. Risk factors predicting lack of immunization in children with measles in stepwise logistic regression were black ethnicity, urban residence, poor prenatal care, preschool age, and an unknown father. Birth certificates contain information that can predict inadequate measles vaccination and should be evaluated prospectively.