Interviewed to obtain the first quantitative data from Scandinavia on lifestyle factors of possible importance for their health were 259 Danish male homosexuals. The frequency of various sex acts, frequency of change in partner, visits to the United States, sexual contacts with victims of the immune suppression syndrome, education, smoking and drug habits, and recent medical problems were recorded. Of those interviewed, 170 were from the Danish capital, Copenhagen, and 89 were from a smaller provincial town, Aarhus. Sexual habits and most other factors were very similar in men from the two cities. Furthermore, the sex habits of those who had visited a venereal disease clinic were similar to those of the group as a whole except for a frequent change of partners. Our data on level of sexual activity resemble those available for the San Francisco Bay area of 1970. The Copenhagen men, however, had more partners per year, had more sexual contact with U.S. citizens and immune suppression syndrome victims, and more had used nitrite inhalation than the men in Aarhus. The frequency of venereal disease was the same in the two groups, but the Danish cases of Kaposi's sarcoma and the acquired immune deficiency syndrome all have come from the Copenhagen area. Two of those interviewed have developed AIDS subsequent to homosexual contact with a case of Kaposi's sarcoma.