National policies for chemoprophylaxis after single cases of meningococcal disease in day-care or nursery settings vary across Europe. We carried out a multi-national retrospective study to compare the effectiveness of different policies. Countries were divided into those recommending chemoprophylaxis only to close contacts (policy A, close) and those recommending chemoprophylaxis for all children in the same nursery (policy B, mass). Country-specific relative risk (RR) of a cluster was defined as the ratio of the number of clusters observed to the number of clusters expected by chance. In total, 37 clusters were identified between 1 January 1993 and 31 December 2002. After adjusting for marked heterogeneity in RR by country, the ratio of RR between countries suggested possible benefit from mass prophylaxis (RR ratio 3·8, 95% CI 0·7–22·0), although the difference was not statistically significant (P=0·22). The costs of this approach and the low risk of clustering need to be taken into account when deciding national policy.