To determine the risk of Hemophilus influenzae type b disease among children attending day-care facilities who were exposed to a primary case of invasive hemophilus disease, we conducted a two-year (August 1982 through July 1984) statewide prospective study involving active surveillance for H. influenzae disease and a 60-day follow-up of the children's day-care contacts. We identified 185 patients with primary invasive hemophilus type b disease who were under six years of age and who attended a total of 195 day-care facilities (centers or private homes). There were 4102 children in attendance at these day-care facilities when the primary cases occurred; 4034 (98 percent) were followed for 60 days or more after the onset of illness in the patients with primary disease. A total of 2612 children were considered classroom contacts of the patients with primary disease, because they were cared for in the same home or the same room in a larger facility, but they were not siblings of the index patients. Of these classroom contacts, 370 from 0 to 23 months of age and 716 from 24 to 47 months of age did not receive rifampin chemoprophylaxis. We could confirm no subsequent H. influenzae disease among contacts. Our results suggest that the risk of subsequent hemophilus disease in contacts of patients in day-care facilities is significantly lower than that previously reported for siblings and day-care contacts. (N Engl J Med 1987; 316:1–5.) DURING the past seven years, five studies have demonstrated an increased risk of Hemophilus influenzae type b disease among the siblings of patients with primary disease living in the same household.1 2 3 4 5 These studies have demonstrated that among sibling contacts under 48 months of age, the incidence of H. influenzae disease in the 30-day period after the onset of a primary case is 100 to 400 times that found among children in the general population. More recently, investigations of outbreaks of hemophilus disease among children in day-care facilities have suggested that the risk of secondary or subsequent disease for day-care contacts.