"It's about 144 patients plus relatives who were in the current premises", writes Oslo municipality as they now try to track and follow the infection.
The confirmed case is a patient at Legevakten, Oslo's large emergency department at Aker hospital.
Also in Sweden, individual cases have been discovered during the summer.
Measles is highly contagious and was previously a classic childhood disease, but has been rare since vaccinations began in the 1970s and the measles vaccine was introduced in Sweden's general vaccination program in 1982.
In principle, all born before 1960 have had the disease and therefore have lifelong protection.
The symptoms are high fever, dry cough, irritated eyes, and rash. Complications such as pneumonia are common, one in 1,000 gets a serious brain inflammation.
