Chlamydia trachomatis represents an important infectious agent for sexually transmitted diseases. In the USA more than 3 million new cases are recorded per year. The clinical picture and late complications are similar to those of gonorrhea; however, infections from C. trachomatis have relatively mild symptoms. This group of diseases may therefore be overlooked, and complications and late sequelae due to C. trachomatis thus occur more frequently in comparison to N. gonorrhoeae. From the viewpoint of general health in a population, chlamydial infections seem to be more important than the classic venereal diseases. The number of infections may be underestimated as infected individuals may be asymptomatic and are therefore not diagnosed and the disease recorded. Knowledge about chlamydial infections has increased significantly, and C. trachomatis today can easily be diagnosed by routine laboratory methods; this report deals with current knowledge regarding the epidemiology, clinical symptoms, complications, diagnosis, and treatment of genital chlamydial infections.