Estimates of the number of workers in the United States occupationally exposed to beryllium were published in the 1970s and 1980s and ranged from 21,200 to 800,000. We obtained information from several sources to identify specific industries with beryllium exposure and to estimate the number of current workers potentially exposed to beryllium. We spoke with representatives from the primary beryllium industry and government agencies about the number of exposed workers in their facilities. To identify industries in the private sector but outside the primary industry, we used data from the Integrated Management Information System (IMIS), which is managed by the Occupational Safety and Health Administration, and the Health Hazard Evaluation program of the National Institute for Occupational Safety and Health. We used IMIS data from OSHA inspections with a previously developed algorithm to estimate the number of potentially exposed workers in nonprimary industries. Workers potentially exposed to beryllium included 1500 current employees in the primary beryllium industry and 26,500 individuals currently working for the Department of Energy or the Department of Defense. We identified 108 four-digit Standard Industrial Classification (SIC) categories in which at least one measurement of airborne beryllium was > or = 0.1 microg/m3. Based on the subset of 94 SIC categories with beryllium > or = 0.1 microg/m3, we estimated 26,400 to 106,000 workers may be exposed in the private sector (outside the primary industry). In total, there are as many as 134,000 current workers in government and private industry potentially exposed to beryllium in the United States. We recommend that the results of this study be used to target at-risk audiences for hazard communications intended to prevent beryllium sensitization and chronic beryllium disease.