The southern elephant seal population at Macquarie Island has undergone a serious decline since regular surveys were commenced in 1949. Approximately 2,900 cows and 250 bulls were counted in the isthmus study area during the 1985 breeding season. Comparisons with 20 other counts made in the same area between 1949 and 1984 showed that, although there was considerable fluctuation between the years, the number of seals ashore has dropped at an average rate of 2.1% per year, resulting in a net decrease of approximately 50% for both males and females. This is similar to the ratio of decline of elephant seal populations in the southern Indian Ocean. The census information from all major elephant seal populations was reviewed and it was concluded that there may be a common factor, or group of factors, acting to reduce the Macquarie Island and Indian Ocean populations, while the populations of the South Atlantic seem to be stable. Several potential explanations for these observations are advanced, but it is concluded that a greater knowledge of the ecology of the seals is needed if the declines are to be understood.