This study was undertaken to define the factors that enter into the decision to seek care in a pediatric emergency department (ED) during the late evening hours. A questionnaire was administered which sought responses regarding demographic, social/familial, medical, and visit-related information. The questionnaire was completed by 170 nighttime utilizers (11:00 PM to 7:00 AM) and 202 daytime controls. Nighttime users were more likely to have private physicians, were ill for shorter periods of time, were more likely to attempt treatment at home prior to arriving at the ED, tended to use the ED more often, and spent their days outside of the home (in school or daycare), as compared with the daytime controls (P less than 0.05). The average waiting time was longer during the night than during the day (7:00 AM to 5:00 PM). The prime reasons for presenting for care during the night (as well as during the day), according to the caretaker, were illness concerns and not those of convenience.