SummaryIn the context of a surveillance programme for communicable diseases in Belgium, a network of microbiological laboratories takes care, since February 1983, of the weekly registration of a number of pathogenic agents, among whichC. trachomatis.Some epidemiological characteristics°fC. trachomatisin Belgium are discussed. So, more than 75 % of the cases were seen between 20 and 39 years of age, with a maximum for the age group 20–29 years. The ratio men: women wich was equal to 1: 1,1 in 1983–84, is equal to 1: 2,7 in 1986.