In August 2010, the New York City Department of Health and Mental Hygiene (DOHMH) conducted an investigation to identify and provide antibiotic prophylaxis to close contacts of a patient who had died of invasive meningococcal disease. Traditional contact tracing, which relies on interviews with the patient's close associates, identified 3 persons meeting prophylaxis criteria. In addition, DOHMH learned of an Internet site used by the patient to arrange anonymous sexual encounters. By working with the Internet site administrator through a liaison, DOHMH sent notification to 15 additional persons potentially at risk for meningococcal disease; of those, at least 1 met prophylaxis criteria. The Internet has been used previously for partner notification by sexually transmitted disease control programs. This case report illustrates how the Internet can aid contact investigations for other communicable diseases, especially when identifying potential contacts is urgent, patients have died, or contacts are unknown to the patient's associates.