Lymphogranuloma venereum (LGV) is a systemic, sexually transmitted disease (STD) caused by a variety of the bacterium Chlamydia trachomatis that rarely occurs in the United States and other industrialized countries; the prevalence of LGV is greatest in Africa, Southeast Asia, Central and South America, and Caribbean countries. However, in the Netherlands, which typically has fewer than five cases a year, as of September 2004, a total of 92 cases of LGV had been confirmed during the preceding 17 months among men who have sex with men (MSM). The first 13 cases, diagnosed during April-November 2003, were reported by local health authorities in Rotterdam in December 2003. An alert was sent to the Early Warning and Reporting System of the European Union and to the European Surveillance of Sexually Transmitted Infections Network (ESSTI). In April 2004, a report was made to CDC, and state and local health departments were alerted. Of the 92 cases confirmed in the Netherlands, 30 occurred during 2003 and 62 during 2004. This report describes the ongoing investigation of the LGV outbreak. Health-care providers should be vigilant for LGV, especially among MSM exposed to persons from Europe, and prepared to diagnose the disease and provide appropriate treatment to patients and their exposed sex partners.