Hepatic tissues from nine patients who had fatal Rocky Mountain spotted fever were examined in sequential sections by brightfield and immunofluorescence microscopy for histologic lesions and for coincidence of these lesions with the distribution of Rickettsia rickettsii. The basic hepatic lesion in Rocky Mountain spotted fever is an inflammation of the portal triad in which large mononuclear cells and neutrophils predominate. Rickettsia were demonstrated in lesions of the portal triads in eight of nine cases. Inflammation of the portal triad and sinusoidal erythrophagocytosis showed a strong relationship to the presence of the disease state when comparisons with age- and sex-matched control subjects were made. Hepatocellular necrosis was not found to be an important pathologic feature of the disease. Elevated serum bilirubin values and jaundice are likely to be due to a combination of duct obstruction secondary to inflammation and edema of portal triads, and hemolysis.