Non-O1 V. cholerae is a ubiquitous environmental isolate. It is a common contaminant of shellfish, and in the developing world, it is frequently isolated from food and water. Asymptomatic carriage rates approaching 4 percent have been described among persons involved in high-risk activities, such as eating oysters in New Orleans or going on pilgrimage to Mecca. The actual occurrence of disease appears to be much less common. This is an "occupational" pathogen which may be responsible for outbreaks or a high frequency of isolation in certain areas at specific times but which generally ranks as a minor cause of diarrheal disease. While host susceptibility and infectious dose may help explain the relatively infrequent occurrence of non-O1 V. cholerae-associated disease, it also appears likely that only a small minority of strains carry the necessary virulence factors to cause gastroenteritis. Unfortunately, there does not appear to be a single mechanism by which these organisms cause diarrhea; it is likely that we will find a heterogeneous pattern of virulence mechanisms, similar to the heterogeneity seen among diarrheagenic E. coli. As our understanding of these pathogenic mechanisms improves, there should be a corresponding refinement in our understanding of the epidemiology of these widely distributed organisms.