Marijuana use among the 45,000 Air Force troops stationed in Thailand during the period September 1971 to September 1972 was extensive. Nevertheless, only five cases of prolonged psychosis associated with marijuana use in this population were referred for psychiatric evaluation. These cases resembled several types of adverse reactions previously described in the literature: one case of a "marijuana psychosis"; one case of an "organic marijuana syndrome"; and three cases of "marijuana-mobilized functional psychosis." With the exception of the patient with the "marijuana psychosis," this small group of men had either borderline or schizoidal premorbid personalities. Other more transient psychotic episodes appear to go unreported by the troops because of the rapid clearing of symptoms and the punitive policy of the Air Force toward drug abuse.