The relationship between age of asthma onset and behavioral adjustment was analyzed using data from a longitudinal prospective investigation of 150 children identified prenatally as at genetic risk for developing asthma (the W. T. Grant Asthma Risk Study). The children's development and asthma status were monitored regularly for 6 years. Mothers were interviewed yearly using the Behavioral Screening Questionnaire (BSQ). Children who had an early onset of asthma (by 3 years of age) had significantly more behavior problems at age 4 than children who developed asthma later (between 3 and 6 years of age). Furthermore, the early-onset group had significantly more problems at age 6 than both children who developed asthma later and children who never developed asthma. Children with early asthma onset were compared to children who were asthma free on individual problem items of the BSQ, revealing a profile of behavior problems that included waking at night, depressed mood, and some indication of increased fearfulness. This profile is consistent with an earlier report of behavior problems among severely asthmatic preschool children (Mrazek, Anderson, & Strunk, 1984), who displayed the same internalizing behavior problems on the BSQ. These results suggest that early asthma onset may have predictable negative influences on behavioral adjustment over a wider range of asthma severity than has previously been reported.