A total of 439 schizophrenic patients according to ICD-10 criteria was included in an open label postmarketing surveillance study to evaluate the efficiency of resperidone as maintenance treatment of the schizophrenic acute exacerbation. The efficiency of risperidone was assessed according the number of patients who responded to treatment, the duration of the hospitalization period an the decrease in the total score as well as in the different clusters of the Brief Psychiatric Rating Scale (BPRS) during the study period. A patient was considered as responder to treatment when a decrease of, at least, a 20% was achieved in the total BPRS score while being treated in monotherapy with risperidone. Safety was evaluated by the UKU subscale for neurological side effects and spontaneous reports. Patients were evaluated at baseline and weeks 1, 2, 6 and 12. Forty patients (9.1%) were excluded from the statistical analysis due to protocol violation. Eighty one patients (20.3%) dropped out due to lost for follow-up (n = 25; 6.3%), new hospitalization (n = 23; 5.8%), inefficacy (n = 12; 3%), side effects (n = 7; 1.8%) and others (n = 14; 3.5%). Risperidone was used at doses between 1.5 and 19 mg daily (mean dosage: 7.66 +/- 3.07 mg daily). The duration of the hospitalization when dosages of risperidone of less than 6 mg daily were used was 32.1 days. However, when higher dosages were used, the number of days in-hospital decreased (26.6 days at dosages between 6 and 9 mg daily and 25.3 days when dosages higher than 9 mg daily were used). There was a significant reduction, versus baseline, in the BPRS mean total scores as well as in it's different clusters. (positive symptoms, negative symptoms, anxiety/depression) from week one onwards. At week 1, 66.9% of the patients had an improvement (20% versus baseline in their BPRS total score. At the end of the study period, 93.2% of the patients had an improvement (20% in their BPRS total score. There was a significant reduction in the total UKU subscale for neurological side effects scores (p < 0.005) from week 1 onwards, as well as for the total score of the following symptoms: rigidity, hypokinesia, hyperkinesia tremor and akatysia.