This report of the worldwide distribution of two varieties of Cryptococcus neoformans was drawn from data on 628 clinical isolates and from data on 97 additional isolates from other laboratories. Tests showed that 100% of the cultures from Austria, Belgium, Denmark, France, Germany, Holland, Italy, Switzerland, and Japan belonged to C. neoformans var. neoformans. More than 85% of the isolates from Argentina, Canada, the United Kingdom, and the United States (except southern California) were of C. neoformans var. neoformans, the remainder being of C. neoformans var. gattii . There was an unusually high prevalence (35-100%) of C. neoformans var. gattii in Australia, Brazil, Cambodia, Hawaii, southern California, Mexico, Paraguay, Thailand, Vietnam, Nepal, and countries in central Africa. These findings indicated that C. neoformans var. gattii is prevalent only in tropical and subtropical regions. Seventy per cent of the total isolates studied were of serotype A of C. neoformans var. neoformans. Serotype D (9% of the total) was common in Europe, but was found infrequently in other regions. Among the two serotypes of C. neoformans var. gattii , serotype B was 4.5 times more prevalent than serotype C. The majority (88%) of type C isolates in our collection were from southern California.