Lymphogranuloma venereum (LGV) is a sexually transmitted infection (STI) caused by Chlamydia trachomatis (CT) serovars L1, L2, or L3. Common in tropical regions, this infection most often presents as inguinal lymphadenopathy associated with an initial chancre that may go unnoticed. It sometimes manifests as acute proctitis, particularly in male patients who have sex with men. In December 2003, a European alert issued by the European STI Surveillance Network (ESSTI) reported 15 clustered cases of rectal LGV caused by CT serovar L2, which had been diagnosed during the summer of 2003 in the city of Rotterdam. These LGV cases exclusively affected male patients who have sex with men, 13 of whom were HIV-positive. These patients reported having had unprotected sex with various anonymous partners in different European countries, including France. In March 2004, an initial investigation conducted by the French Institute for Public Health Surveillance in collaboration with three Parisian microbiology laboratories and the National Reference Center (CNR) for Chlamydia Infections (University of Bordeaux II) retrospectively identified cases of rectal LGV in France. Among 44 CT-positive rectal samples isolated from male patients in one of the four participating laboratories, 38 (86%) were identified as belonging to type L2, confirming the diagnosis of rectal LGV. The epidemiological survey conducted among physicians who had ordered CT testing for these patients made it possible to trace the clinical history of 14 of these 38 cases. The patient profile was similar to that of Dutch patients. All of these male patients had had sex with men; 8 (57%) were HIV-positive, and 9 (64%) had another STI at the time of diagnosis. They were all symptomatic, with signs of acute rectitis, sometimes severe. Furthermore, the average time between the onset of clinical signs and the diagnosis of chlamydial proctitis was very long (50 days), indicating that this diagnosis had not been considered immediately. To monitor the progression of this emerging trend and characterize the affected populations, a prospective sentinel surveillance system for rectal LGV in France was established in April 2004.