National surveillance for salmonella infections was established in 1962, following recognition of the importance of Salmonella organisms as the cause of potentially preventable infectious disease in the United States. Reports of infections due to Salmonella have risen progressively to approximately 40,000 per year. In contrast, the parallel reporting system for infections due to Shigella shows no such increase. Because a passive surveillance system is used, it has been assumed salmonella infections have been substantially underreported. Three independent methods-determination of carriage rates, calculation of sequential surveillance artifacts, and calculation of overall surveillance artifact-were used to estimate the annual number of salmonella infections in the United States; the results were compared with those of a previous study. These methods produced estimates ranging from 800,000 to 3,700,000 (mean = 1,900,000; median = 1,400,000) infections annually. Accurate assessment of the number of infections is important for determining complication rates and for evaluating the efficacy of control programs.