The Republic of Ireland has the highest incidence of meningococcal disease in Europe with 40% of all cases occurring in children under the age of 5 years. Attending day-care increases the risk of certain infections, including Haemophilus influenzae type b (Hib) meningitis. The risk of meningococcal disease associated with day-care is not known. We conducted a case-control study among pre-school children with 130 laboratory-confirmed cases and 390 controls, matched on age, gender and place of residence, to determine if day-care attendance was a risk factor for meningococcal disease. Multivariate analysis showed that day-care attenders had a lower risk of disease than non-attenders (OR 0.3, 95% CI 0.1-0.7) whereas the number of adults in a household, and household crowding were independent risk factors for disease. Asymptomatic carriers of Neisseria meningitidis are the main source of transmission and these carriers are usually adults. Regular day-care attendance may reduce this risk by removing children from close and prolonged contact with adults.