Influenza vaccination is recommended for children with moderate to severe asthma. However, most children with asthma are not vaccinated, in part because many do not make an office visit during the vaccination time period. We studied 247 urban children with asthma to determine the maximum number that could have been vaccinated during a medical visit to a clinic or emergency department. One hundred thirty-nine patients (56%) had at least one visit during the study period. Sixty-five patients (26%) received the influenza vaccination; 74 patients (30%) did not receive the vaccination despite being seen in the clinic or emergency department. One-half of the missed vaccination opportunities at the clinic occurred during nonacute visits. Influenza vaccination rates could be substantially improved by efforts to increase primary care visits during the vaccination time period and to minimize missed vaccination opportunities.