We have prospectively studied 158 cases of acute hepatitis delta observed during the last 7 years in a general hospital. Among them 136 were male and 22 female. The mean age was 22.7 years with a range between 16 and 61 years. The epidemiologic factors were drug addiction by parenteral route in 145 cases (92%), sexual transmission in 5 (3%), post transfusional in 2 (1%) and unknown in 6 (4%). With respect to the delta type infection, 105 cases (66%) were coinfections with type B and delta, and 53 patients had a type delta superinfection (34%). The clinical course was a fulminant hepatitis in three cases (two cases of coinfection B and delta an one case of delta superinfection), and an acute benign hepatitis in 155 patients. The follow-up of 118 patients revealed that 96% of coinfections by type B and delta evolved to the chronicity showing findings of active chronic hepatitis or hepatic cirrhosis. It should be noted that in 4 cases of superinfection delta type (11%) the HBsAg was negative after several months of positivity. In these patients the level of transaminases normalized and the hepatic histology evidenced alterations of chronic active hepatitis (2 cases) and hepatic cirrhosis (2 cases) without identification of tissular delta antigen.