Between September 23 and November 30, 1981, 1,032 children from Panamá City, Republic of Panamá were hospitalized with aseptic meningitis. Forty-four per cent of the cases were in the age group 5-9 years old; the disease was mild and self-limiting with an average hospital stay of five days. Echovirus 4 isolates were obtained from 48 of 160 patients. To identify risk factors associated with the epidemic, the authors randomly selected 10 per cent of hospitalized cases and conducted a family-based seroepidemiologic study. The closest neighboring house with at least one child younger than 15 years was similarly studied as a control. In total, 182 households and 1,083 of 1,177 residents were included. No risk factors ascertained by the study were associated with aseptic meningitis; however, several factors were related to recent echovirus 4 infection. Overall, 56 per cent of cases had echovirus 4 antibody, as did 29 per cent of their family members and 19 per cent of control family members. Children who attended kindergarten or primary school were more likely to have antibody than other household members and, within case families, individuals involved in child-care had an excess risk for infection.