The prevalence and trends of pulmonary nontuberculous mycobacteria (NTM)-associated hospitalizations in the United States were estimated using national hospital discharge data. Records were extracted for all persons with a pulmonary NTM International Classification of Diseases code (031.0) hospitalized in the 11 states with continuous data available from 1998 through 2005. Prevalence was calculated using US census data. Pulmonary NTM hospitalizations (031.0) increased significantly with age among both sexes: relative prevalence for persons 70-79 years of age compared with those 40-49 years of age was 15/100,000 for women (9.4 vs. 0.6) and 9/100,000 for men (7.6 vs. 0.83). Annual prevalence increased significantly among men and women in Florida (3.2%/year and 6.5%/year, respectively) and among women in New York (4.6%/year) with no significant changes in California. The prevalence of pulmonary NTM-associated hospitalizations is increasing in selected geographic areas of the United States.