The objective of the present study was to compare the efficacy and adverse effects of olanzapine plus fluvoxamine and those of olanzapine alone, in schizophrenic patients with acute exacerbation. A randomized, placebo-controlled, 6-week trial was carried out at a University Hospital in Bangkok, Thailand. The efficacy and adverse effects were assessed biweekly by using the Brief Psychiatric Rating Scale (BPRS) and the Udvalg for Kliniske Undersogelser side-effect scale, respectively. Twenty schizophrenic patients with acute exacerbation were randomly assigned to receive olanzapine plus fluvoxamine or olanzapine alone. The study found that the means of BPRS total and BPRS general psychopathology score changes were significantly larger in olanzapine plus fluvoxamine group (P= 0.037 and P= 0.045, respectively). The incidence of treatment adverse effects is comparable. In conclusion, the study findings suggest that fluvoxamine augmentation to olanzapine is well tolerated and more effective than olanzapine alone for short-term (6-week) treatment of an acute exacerbation of schizophrenia. Due to a number of limitations, further studies are warranted to confirm.