A total of 519 cases of viral hepatitis were admitted to the Infectious Diseases Hospital from June to October 1982 during an epidemic in Rangoon; 399 cases were found to be hepatitis non-A non-B, 84 cases were hepatitis B and 36 cases were hepatitis A. A clinical study was done of the 399 non-A non-B hepatitis cases. Also a prospective study of 434 households made up of 217 non-A non-B hepatitis cases with their families, together with 217 matched control families were followed up for a period of seven months to detect secondary cases among the family members. Non-A non-B hepatitis was found to occur most in adults of 20–40 years. Non-A non-B hepatitis is indistinguishable from the other two types of viral hepatitis. Case fatality rate was the highest in pregnant women with non-A non-B hepatitis. The field study suggested non-A non-B hepatitis can be transmitted by intrafamily spread. No evidence of sexual or syringe transmission of non-A non-B hepatitis was found.