Eleven narcotic injectors from a prison in Saigon were hospitalized with falciparum malaria. Coma and intense parasitemia were common and eight patients died soon after admission. Two of three autopsied cases also had purulent pulmonary infections. No non-addicted prisoners were hospitalized for malaria. Nine more unsuspected falciparum infections were found among 29 other addicts in the prison. The clustering of malaria infections among narcotic injectors who had not been in malarious areas indicates that the malaria was transmitted by the common use of needles and syringes. Cerebral malaria in an addict may be misdiagnosed as drug intoxication. Malaria surveillance is recommended for the increasing addict population in the cities of Southeast Asia.