Scandinavia (Denmark, Finland, Iceland, Norway, and Sweden) comprises with mutual borders and 22.3 million inhabitants an area where the socioeconomic and cultural conditions are similar. Epidemic diseases, such as meningococcal infection, might therefore be expected to be uniformly distributed. An epidemiological study in the 10-year period 1970-9 shows, however, remarkable differences in the incidence, age, and serogroup and type distribution, as well as in the general dynamics of the disease. Three epidemics, two caused by different serotypes of group B (Norway and Iceland) and one by group A (Finland) occurred within the observation period. The annual overall incidence was generally around 3/100 000 but increased from fivefold (Finland) to eightfold (northern Norway) during epidemics. The epidemic strains caused infection in over 3000 patients and the loss of at least 250 lives. The overall case fatality rate was 8.6% (range 4.1-13.7%). Men were more susceptible and had a worse prognosis than women of the same age group. The group A epidemic in Finland was influenced by a large vaccination campaign, but this possibility was not feasible in the two other epidemics.