The possible adverse clinical effects of untreated psychosis in schizophrenic patients, particularly early in the course of illness, have been a topic of considerable interest in recent years. We examined the timing of first administration of antipsychotic medication after the first onset of psychotic symptoms in 103 patients with DSM-III-R diagnoses of schizophrenia, schizophreniform or schizo-affective disorder. Patients with a delay of one or more years between the onset of the first psychotic symptom and the initiation of antipsychotic treatment demonstrated more severe negative symptomatology on admission to hospital and more severe positive symptoms and negative symptoms at discharge. These effects were present in both first-admission patients, in whom the delay to treatment immediately preceded hospitalization and chronic patients with a history of multiple hospitalizations. Patients with one or more years of untreated psychosis prior to their first antipsychotic treatment displayed a more severe poverty syndrome at the time of admission and discharge and a more severe reality distortion syndrome at discharge from the index hospitalization. These findings were not related to age, premorbid functioning, duration of illness, first- vs multiple-episodes status, or dosage of antipsychotic medication at time of admission or discharge assessment. Findings from the present study suggest that failure to initiate antipsychotic treatment early in the course of the illness may be associated with a recurrent pattern of poorer treatment response and more severe and persistent positive and negative symptomatology. These findings indicate the importance of early detection of illness and early initiation of antipsychotic treatment for the first psychotic symptoms of schizophrenia.