Fewer than 10% of children with moderate or severe asthma receive an annual influenza vaccination despite their heightened susceptibility to severe infections and recommendations by the American Academy of Pediatrics and the Immunization Practices Advisory Committee that all such children be vaccinated annually. Patient, provider, and system factors leading to this poor vaccination rate are not well understood. This study tested the effectiveness of a computerized reminder system in improving influenza vaccination rates in children with asthma and examined patient barriers to vaccination at one pediatric clinic in an urban teaching hospital. A computer database identified 124 children with moderate or severe asthma. Patients were randomly assigned either to study group (n = 63), who were sent a personalized letter reminder about the need for an influenza vaccination, or to a control group (n = 61), who received no reminder. Study group mothers were interviewed 2 months after the letter was sent to assess factors associated with receipt of vaccination, including demographic features, parental worry about asthma and vaccine side effects, the four dimensions of the Health Belief Model, and health locus of control beliefs. Nineteen study group patients (30%) received an influenza vaccination, compared with only 4 control patients (7%) (P < .01). Forty-three mothers of children in the study group were interviewed; 14 (33%) of these children had received the vaccination. Of the characteristics investigated, two significantly correlated with vaccination compliance: high levels of parental worry about asthma (positively correlated: odds ratio = 23.3, P < .01) and high levels of parental worry about vaccine side effects (negatively correlated: odds ratio = 0.087, P = .025).(ABSTRACT TRUNCATED AT 250 WORDS)