The number of patients reported th have disease due to Mycobacterium kansasii or M intracellulare-avium has increased in Texas from January 1967 to December 1976, in contrast to a decrease in tuberculosis. Presented is an analysis of 1,409 patients infected with M kansasii and 706 patients infected with M intracellulare-avium. The former group clustered in urban areas with more than twice the incidence compared to nonurban areas (P less than 0.001). The latter group was more diffusely distributed with approximately twice the incidence in nonurban areas compared to urban areas (P less than 0.001). The average age of the group infected with M kansasii was 50 years and of the group infected with M intracellulare-avium 58 years. In patients infected with M kansasii only, the average age was significantly higher for men than women. There was a male predominance in both groups, ie, 3:1 in M kansasii and 2:1 in M intracellulare-avium. Persons with Spanish surnames had a low incidence of disease due to M kansasii. No other racial or ethnic association was noted. The various factors involved in determining the atypical mycobacterial diseases are discussed.