The occurrence of acute otitis media (AOM) has increased steadily during the last 15 years. The possible environmental risks associated with AOM should be well identified to prevent any further increase in its occurrence. A meta-analysis of the studies evaluating the risk factors for AOM was performed. A MEDLINE search of the medical literature from 1966 to 1994 with the key words children, risk, acute otitis media, and recurrent acute otitis media was performed, and the references of the articles that were found served as the sources for the studies used in the meta-analysis. Sixty-one studies were identified. Twenty-two (36%) of these studies were accepted for the meta-analysis. Depending on the risk factor, there were two to seven different studies from which risk ratios (RRs) could be pooled. The studies were performed in six different countries. If any other member of the family had had AOM, the risk increased (RR, 2.63; 95% confidence interval [CI], 1.86-3.72; P = .00001). The risk of AOM increased with day care outside the home (RR, 2.45; 95% CI, 1.51-3.98; P = .0003) and family day care (RR, 1.59; 95% CI, 1.19-2.13, P = .002). The risk of AOM increased with parental smoking (RR, 1.66; 95% CI, 1.33-2.06; P < .00001). Breast-feeding for at least 3 months reduced the risk of AOM (RR, 0.87; 95% CI, 0.79-0.95; P = .003). The use of a pacifier increased the risk of AOM (RR, 1.24; 95% CI, 1.06-1.46; P = .008). Child care outside the home and parental smoking were the factors that most significantly increased the occurrence of AOM