Many specific and nonspecific items have been implicated in the etiology of primary hepatic cancer. These include hepatic cirrhosis,1,2 parasites,3 inflammation,4 mechanical irritation,5 malnutrition,6 liver cell rests,7 and toxic substances.8 To the latter group, colloidal thorium dioxide (Thorotrast) must be added. There are now 45 published cases of primary hepatic cancer which occurred in patients who received intravascular injections of colloidal thorium dioxide.9 From 1941-1949 colloidal thorium dioxide was almost the exclusive contrast medium used for cerebral arteriography in this country. A study of the incidence of primary liver cancer in these patients will be done by the Division of Radiological Health of the United States Public Health Service. Since colloidal thorium dioxide was used as a diagnostic tool in the evaluation of neurologic disease, it was of interest to determine whether neurologic disease is associated with liver cancer. An extensive review