Aseptic meningitis is an inflammation of the tissues covering the brain and spinal cord and caused by a virus, most frequently an enterovirus. In August 2003, the Connecticut Department of Public Health (CDPH) received a report of three viral meningitis cases among recreational vehicle (RV) campers staying at a campground in northeastern Connecticut. CDPH, assisted by CDC, conducted an investigation, which 1) identified a total of 12 cases of aseptic meningitis and 24 cases of enterovirus-like illness among 201 campers interviewed, 2) demonstrated how transmission of enterovirus from persons with mild illness contributed to the aseptic meningitis outbreak, and 3) determined that crowded conditions inside RVs and in the campground swimming pool likely facilitated spread of enterovirus. Pool operators should check chlorine and pH levels frequently, particularly during peak pool occupancy; adults should take precautions against passing enterovirus to children, who are at greater risk for severe illness.