The case history of an unvaccinated 14-year-old girl with trisomy 21 and an unrecognized, lethal measles infection is reported which was belatedly only diagnosed postmortem. On the basis of the medical history, a pharmaceutically induced exanthema was initially suspected after the differential diagnosis. The diagnosis of measles was ultimately based on a positive genetic test, as well as on serological and histological tests. Measles is a notifiable infectious disease, and this case underlines the relevant regulations in the Infection Protection Act. The case also documents the still prevailing problems in the discussion about the necessity of a comprehensive immunization coverage.