OBJECTIVE: The aim of this study was to examine the relationship between depersonalization induced by tetrahydrocannabinol (THC), and regional brain activation. METHOD: Cerebral blood flow (CBF) was measured by means of positron emission tomography (PET) in 59 normal right-handed volunteers before and following intravenous infusions of THC. RESULTS: After THC, CBF showed a global increase which was more marked in the right hemisphere, frontal lobes and anterior cingulate. CONCLUSION: Regression analyses showed positive correlations between the right frontal and anterior cingulate and depersonalization.