Eighteen newly diagnosed cases of symptomatic cocidioidomycosis developed two to four weeks following exposure to a severe natural dust storm. The population at risk consisted of 26,000 residents of the San Joaquin Valley with access to health care at the Naval Hospital, Lemoore, Calif. Eight patients were white, and ten were nonwhite. The number of cases per 100,000 was estimated to be 36 for the white group and 254 for the nonwhite group. The disease was disseminated in four patients, and all were from the nonwhite group. One patient with disseminated disease, a black man, died. These data suggest that nonwhites may be relatively more susceptible to acquiring primary disease, in addition to developing disseminated disease. Dust storms of this magnitude must be considered a threat to health for populations living within areas endemic for coccidioidomycosis.