That the roentgenographic appearance of pulmonary coccidioidal infection may closely simulate that of pulmonary tuberculosis has been pointed out repeatedly, particularly by Smith,1 Yegian and Kegel2 and Farness and Mills.3 When pulmonary cavitation occurs the mimicry is even more striking, and confusion in diagnosis may follow unless the causative organism is first isolated and identified. It would appear, however, that such parallelism between the two infections exists only in roentgenograms. Coccidioidal cavitation, as demonstrated in the 13 cases reported in this paper, is far more benign than is pulmonary cavitation due to tuberculosis. Unlike the latter condition, which usually occurs during reinfection or in the adult type of the disease, most coccidioidal cavitation develops during or shortly after the primary stage of pulmonary infection. This belief was also expressed by Farness and Mills in their first report of a case of pulmonary cavitation due to coccidioidal infection.