• The initial clinical symptoms of 25 consecutive cases of cannabis psychosis of the paranoid type and 25 consecutive cases of paranoid schizophrenia were studied and compared, in order to delineate features that would enable a differentiation of the two conditions. It was observed that the patients with cannabis psychosis substantially differed in terms of behavioral manifestations. Most of these patients were violent and panicky and demonstrated bizzare behavior, but they possessed some insight into the nature of their illness. Schizophrenic patients manifested these disturbances and characteristics less frequently. Subjects with cannabis psychosis showed rapid ideation and flight of ideas, whereas the characteristic schizophrenic thought-disorder was found mostly in schizophrenic patients.