Incidence of spontaneous pneumothorax in Olmsted County, Minnesota: 1950 to 1974.

Between 1950 and 1974, 318 cases of initial pneumothorax were diagnosed among the residents of Olmsted County, Minn. Seventy-five cases were due to trauma, and 102 were iatrogenic. One hundred forty-one cases were spontaneous in onset, of which 77 were primary and 64 secondary to a specific underlying pulmonary disease. The age-adjusted incidence of primary spontaneous pneumothorax was 7.4/100,000/yr for males and 1.2/100,000/yr for females. For secondary spontaneous pneumothorax, the incidence was 6.3 and 2.0/100,000/yr for males and females, respectively. The ratio of male-to-female incidence was 6.2:1 for primary and 3.2:1 for secondary spontaneous pneumothorax. The differences between the incidence rates for primary and secondary pneumothorax by sex or in total were not significantly different.