To assess the prominence, persistence, and prognostic significance of positive thought disorder in schizophrenia, we studied a large sample of psychiatric inpatients at the acute phase and then followed them up twice--1 1/2-2 years and 4 years after hospital discharge. Positive thought disorder was more prominent at the acute phase in schizophrenic and manic patients than in other types of psychotic and nonpsychotic disorders. At followup, positive thought disorder did not persist for all schizophrenics, but a significantly larger percentage of schizophrenic than other psychotic and nonpsychotic patients followed a course in which positive thought disorder was either persistently or episodically present. Positive thought disorder, when seen after the acute phase, was related to concurrent functioning, and predicted subsequent poorer outcome and functioning for both schizophrenic and nonschizophrenic patients. Positive thought disorder was one of several central features of the active schizophrenic disorder. Among schizophrenics, it was related to other major types of psychopathology, especially delusions, another positive symptom with cognitive-ideational elements. Severe positive thought disorder after the acute phase indicated a sustained episode, and suggested a more severe type of schizophrenia with a poorer prognosis.