Bovine leukemia virus (BLV) is now present in almost all US dairy herds, and the prevalence among cattle in our milking herds is now approaching 50%. Most dairy producers know that BLV can cause tumors in a small percentage of cattle, but the associations now being observed with reduced milk production and cow longevity are not yet appreciated by most dairy producers. Over 20 nations have eradicated BLV from their cattle populations by removing all antibody positive animals. This is economically impossible for all but a small percentage of farms that have very low BLV prevalence. Management interventions to reduce transmission have not been promising. New diagnostic methods may be helpful to better target culling and segregation to those animals that are most infectious to herd mates. Producers interested in determining BLV prevalence in their herd are advised to conduct a BLV herd profile, which involves milk or serum ELISA testing of the 10 most recently calved cattle in lactations 1, 2, 3, and 4+. More information is available on our website at www.BLVUSA.com.