Measles virus genotype B3 was isolated from patients during a measles outbreak in Copenhagen starting January 2006. Here we describe three cases: two children aged 9 and 22 months, respectively, and a 29-year-old man. All three patients were hospitalised. Several doctors examined both the children before the diagnosis of measles was established. The patients were not vaccinated against measles. They had not been abroad within the last three weeks. Genotype B3 is endemic in West and Central Africa. The genotype B3 detected in these cases was different from the B3 seen in recent outbreaks in Europe.