New cases of acute primary coccidioidomycosis in large numbers resulted from a windstorm that blew through Kern County, California, on December 20, 1977. In most of these cases clinically apparent infections developed in early and mid-January 1978 and occurred not only in persons exposed directly to the dust raised by the windstorm but also among those in many areas to the north and west of Kern County. The exposure to the dustborne Coccidioides immitis was brief because of the arrival of drenching rains, but the continued heavy rainfall increased the potential for large numbers of cases of coccidioidomycosis to occur in the summer-fall season.