To determine the infectivity of Crimean-Congo hemorrhagic fever (CCHF) virus via routine contacts between serologically confirmed cases and their close relatives from May 2005 up to March 2006, 79 serum samples of 57 close relatives of 12 newly diagnosed serologically confirmed CCHF cases in the Sistan-va-Baluchestan province of Iran were tested for IgG and IgM antibodies against CCHF virus using the enzyme-linked immunosorbent assay technique. Nine levels of contacts were considered: percutaneous contact with the patient's blood, cutaneous contact with the patient's blood, cutaneous contact with non-sanguineous body fluids, cutaneous contact with the patient's skin, sexual contact, eating at the same table, being a roommate of the patient, being a housemate of the patient, and living with the patient in the same building. Only one out of 57 relatives was positive for anti-CCHF IgG (1.8%, 95% confidence interval 0.0 to 9.8%). Thus, the infectivity of the virus via usual routine contacts with patients appears to be low.