The occurrence of otitis media was studied in 108 Sweden children attending 14 day-care centers and compared with that in 57 children cared for in their own homes (usually with one or no sibling) and with that in 42 children in family day-care homes (where a woman cared for both her own and 1 to 4 other children in her home during the day). The children were 6 months to 2 years old. In the day-care centers 37% of the children had otitis media at least once during 8 months with an average of 2.2 episodes each. Otitis media was more common in 6- to 17-months-old children in the day-care centers than in children of the same age cared for in their own homes. The occurrences of otitis media in the day-care centers and in the family day-care homes were approximately equal. Children attending centers where those with signs of infection were excluded had otitis in about the same frequency as those attending centers where children with infections were accepted.