Meningococcal disease (MD) remains an important health problem. Crowding has been suggested to be a risk factor for MD in children, but the evidence is relatively sparse. We performed a nationwide nested case-control study comprising 1222 children with MD and 24,549 population controls. We identified MD cases younger than 6 y in the Danish National Hospital Discharge Registry from 1980 to 1999, and obtained information on household density as a measure of crowding, per capita income and other potential confounders through The Danish Civil Registration System and social registries. The risk of MD associated with household density was estimated by conditional logistic regression for children less than 1 y of age (infants) and children aged 1 to 5 y, respectively. The risk of MD increased with increasing household density. In both age groups, the crude OR was 1.8 (95% confidence interval [CI]: 1.4-2.3) at a density of less than 20 m2 per person compared with the reference of more than 50 m2 per person. The adjusted OR for MD was 1.5 (95% CI: 1.1-1.9) for infants, and 1.5 (95% CI: 1.1-2.0) for children older than 1 y. Household density appears to be a risk factor of MD in preschool children.