It is presented an epidemiological summary of epizootic yellow fever outbreak happened in 1973. Its incidence, the distribution according to ages, to sex and geographical distribuion are pointed out. The results of the revision of yellow fever cases, which have been studied, collected and archived in viscerotomy Service collection of Histopathology of Yellow section of Oswaldo Cruz Institute, since 1931 are presented. The article is ilustrated with tables and graphics which registrate the data indicated above. The authors emphasize the following items: 1) Urban and jungle yellow fever present epidemiological aspects completely different; 2) Jungle yellow fever incidence occurs mainly in mate according to statiscally significant data; 3) The most hitted age band in the jungle form is between 20 and 30 vears. 4) The jungle yellow fever continues in enzootic areas along water courses; 5) It seems to exist a relation between climatic conditions and yellow fever incidence. 6) The yellow fever cycle is about 7 years. 7) The vaccination program and viscetomy services of SUCAM are of maximum value.