Previous surveys of stroke populations have offered only cursory information on language disturbance, and, conversely, few surveys of aphasic populations have dealt exclusively with stroke or with acute phenomena. This paper describes aphasia in 850 acute stroke patients consecutively registered by the Harlem Regional Stroke Program, of whom 177 (21%) were aphasic; of these, nine were of Broca's type, 24 were of Wernicke's type, 14 were anomic, ten were conduction, seven were of "isolation" type, and 107 were "mixed." An unexpected finding was a significant overrepresentation of men among the nonfluent aphasics. During the following four to 12 weeks, 12% of fluent aphasics died, and 12% remained moderately or severely impaired; among survivors, aphasia improved in 74%, and in 44% it cleared completely. During the same period, 32% of nonfluent aphasics died, and 34% remained moderately or severely impaired; among survivors, aphasia improved in 52%, and in only 13% did it clear completely. In both fluent and nonfluent groups, hemiparesis and/or visual field cut were associated with poor prognosis.