The unusual epidemiology of beryllium disease observed in the early studies of beryllium disease led in 1951 to the hypothesis that the chronic form of the disease is the result of an acquired sensitization to beryllium or its compounds. After 30 years, the role of sensitization has been confirmed in a number of laboratory and clinical studies. The unusual epidemiological features first summarized by Sterner and Eisenbud continue to be evident. The early studies also led to formulation of standards that have resulted in effective control of both the acute and chronic pulmonary forms of beryllium disease. No case of acute chemical pneumonitis has been reported among beryllium workers in about 15 years, and the number of chronic cases has diminished greatly despite a marked increase in the use of beryllium.