Surveillance of trends in Chlamydia trachomatis (Ct) infections in France is conducted by a network of volunteer laboratories known as Rénachla. Since early 2000, there has been a steady annual increase in the number of Ct infection diagnoses. From 2006 to 2009, increases were observed in all indicators: the number of people tested, the number of positive diagnoses, and the positivity rate. The increase in each of these three indicators is more pronounced among women (+63%, +113%, and +31%, respectively) than among men (+39%, +58%, and +14%, respectively). The proportion of screenings (CT infection diagnoses) performed on asymptomatic individuals has risen sharply over the past decade. While fewer than one-third of cases were asymptomatic in 1998, more than two-thirds of cases were asymptomatic in 2009 (women: 64%, men: 68%). This increase in testing was observed over the 2006–2009 period primarily in the Centers for Anonymous and Free Testing (CDAG) and in the Family Planning and Education Centers (CPEF). The high positivity rate observed in laboratories working with CDAGs (9.4%) supports the conclusions of the ANAES report, which recommended in 2003 that screening efforts prioritize young people seeking care at these types of facilities. (R.A.)