Encephalitis, particularly herpes simplex encephalitis, frequently presents as a disorder with puzzling psychiatric symptoms before frank evidence of central nervous system involvement is apparent. The author describes three cases of encephalitis characterized by abrupt onset of bizarre psychological disturbance in the absence of gross neurologic dysfunction. Each patient was initially diagnosed as schizophrenic but later became critically ill and recovered only after a long and chaotic hospital course. The author warns psychiatrists and staff on psychiatric impatient units against mistakenly diagnosing cases of early encephalitis as functional psychoses.