The proportion of cases with fresh syphilis in males contracted by homosexual contacts in Helsinki before and after the change of the criminal law in 1971 was studied. Since 1971, homosexuality is by law no longer a crime in Finland. In 1964, only 2% of males with fresh syphilis admitted a homosexual contact. The same figure was 8% in 1970, and increased to about 50% in 1974 and 1975. It was concluded that a change of legislation concerning homosexuality, probably by several different routes, changed the proportion of cases of detected homosexually transmitted early syphilis. This was thought to be of special importance for case finding and controlling of the spread of syphilis.