Imported infectious diseases in the Departments for Epidemic Diseases in Blegdams Hospital and the University Hospital, Copenhagen, are reviewed for the period 1975-1986. A total of 3,454 cases were diagnosed. 92% were due to parasitic infections. 20.2% of the diagnoses were made i Danes. 38% of these had malaria. Ancylostomiasis, ascariasis and trichuriasis constituted 55% of the diagnoses and were found mainly in boat refugees from Vietnam. Africa, south of Sahara, Asia and the Mediterranean countries were the commonest sources of infection. The number of diagnoses increased tenfold as compared with the period 1965-1974 and this was due mainly to immigration of 3,000 boat refugees from Vietnam during the period 1979-1983. The number of danes averaged 57 annually. Only a slight increase occurred in imported infectious diseases in Danes as compared with the period 1965-1974. Malaria, bacterial and parasitic intestinal infections were the commonest diagnoses in this group. The next largest group of patients consisted of immigrants from Pakistan and Turkey. During the period 1979-1983, 79% of the diagnoses were made mainly in the boat refugees from Vietnam. The individual diseases are reviewed and the possibilities for prevention of imported disease are outlined.