Rubella is a public health problem due to the teratogenic effects associated with primary rubella infection during pregnancy (congenital rubella syndrome). Following universal rubella vaccination of infants in the Netherlands, the incidence of rubella has declined dramatically. However, since September 2004, an outbreak has occurred among unvaccinated individuals, most of whom declined vaccination based on religious beliefs. In the period 1 September 2004-22 March 2005, 166 cases of rubella were reported, including 12 pregnant women. Monitoring for signs that the epidemic has spread to other populations in the Netherlands is important because this might indicate the need for additional interventions. Awareness among health-care workers of the possible occurrence of congenital rubella syndrome should be raised. The clinical manifestations of congenital rubella syndrome are diverse, can be transient or permanent, and may not present until adolescence or adulthood. All cases of laboratory-confirmed rubella infection and congenital rubella syndrome should be reported to municipal health authorities. There is a possibility that this outbreak will spread abroad. The WHO aims to reduce the incidence of congenital rubella syndrome to < 1/100,000 live births. Health-care workers in the Netherlands should be extra alert to detect and notify rubella in a timely manner.