This article compares the effects of short- and long-term treatment with haloperidol in schizophrenic patients, with the aim of identifying brain metabolic activity patterns common to acute and chronic patients in spite of their different treatment and illness duration. [18F]fluoro-deoxy-glucose (FDG)-positron emission tomography (PET) studies in the resting condition were performed on 18 healthy controls and two groups of schizophrenic patients: recent onset (RO, n=17) minimally treated with haloperidol, and chronic long-term treated patients (LT, n=34). PET scans were analyzed using statistical parametric mapping (SPM'99) and the P-value threshold to assess differences between groups was validated by bootstrapping techniques. Our results show a distinctive pattern of decreased activation of the visual cortex in RO and LT patients, when compared to healthy controls. Insular hypometabolism and a certain degree of hypofrontality were observed in the LT group when compared to RO patients. The main effect of the long-term administration of haloperidol seems to be an increase of cerebellar, basal ganglia and motor area metabolism.