Studies of 1986-1995 revealed diseases etiologically connected with California serogroup viruses (Bunyaviridae, Bunyavirus) all over the country. Highly endemic zones are the tundra, taiga, and leafy forest. The disease occurs mainly in summer, the patients are mostly young: under 30 years of age. Analysis of 183 cases confirmed by laboratory findings enabled us to distinguish the following forms: influenza-like (70.9%) with the predominant involvement of the bronchopulmonary system (bronchitis and pneumonia) and neuroinfection (20.2%) (serous meningitis and meningoencephalitis).