In the Scandinavian countries, laws require reporting of the traditional venereal diseases, i.e., gonorrhea, syphilis, lymphogranuloma venereum (LGV), and ulcus molle, or chancroid. Incidence figures for these diseases, therefore, are fairly reliable. In the Scandinavian countries, LGV and chancroid are rare diseases, and the syphilis incidence has remained low. These three diseases are typically male afflictions. Gonorrhea outnumbers the other diseases mentioned and at present has a nearly 1:1 male: female ratio. In Scandinavia, as in other parts of the world after World War II, gonorrhea has shown great epidemiological fluctuations. A heavy increase in its incidence was evident in Sweden and Denmark during the 1960s. During the 1970s, however, the incidence in Sweden dropped significantly, with the 1980 figures corresponding to those seen in 1960. Sweden now has the lowest incidence of gonorrhea among the Scandinavian countries. During the past three years, the incidence of infections with penicillinase-producing gonococci (PPNG) has increased. Most of the strains isolated have originated from the Far East. As documented in several recent investigations, genital chlamydial infections are at least as common as gonorrhea in the Scandinavian countries. Acute salpingitis has been shown to be a common complication of such infections. Among the other sexually transmitted diseases (STD), Trichomonas infections are still common. The prevalence of genital warts and of Herpes Simplex Virus (type 2) infections is increasing and within the next few years these probably can be expected to become an even greater problem than are the traditional venereal diseases, because no specific treatment is yet available.