Tularemia is a zoonotic disease caused by the gram-negative coccobacillus Francisella tularensis. Known also as "rabbit fever" and "deer fly fever," tularemia was first described in the United States in 1911 and has been reported from all states except Hawaii. Tularemia was removed from the list of nationally notifiable diseases in 1994, but increased concern about potential use of F. tularensis as a biological weapon led to its reinstatement in 2000. This report summarizes tularemia cases reported to CDC during 1990-2000, which indicate a low level of natural transmission. Understanding the epidemiology of tularemia in the United States enables clinicians and public health practitioners to recognize unusual patterns of disease occurrence that might signal an outbreak or a bioterrorism event.