Hemicraniectomy is increasingly used as treatment option in stroke and in head trauma, but little is known on the (patho)physiological regional effects of hemicraniectomy in the normal brain. A standard left-sided craniectomy was performed in three cats. Regional cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO(2)) and cerebral metabolic rate of glucose (CMR(glc)) were measured from the brain tissue underneath the craniectomy at 2, 20 and 28 h after hemicraniectomy. CBF significantly decreased (P<0.01) and oxygen extraction fraction (OEF) (P<0.05) significantly increased. CMRO(2) and CMR(glc) decreased only in regions with most severe CBF reduction. These effects remained for at least a day irrespective of corrective sustaining cranioplasty. The authors demonstrated for the first time that decompressive hemicraniectomy in the cat decreases CBF, and to a lesser extent CMR02 and CMR(glc) 2 h after hemicraniectomy in normal brain tissue that last for at least 1 day. Even though the underlying basis of these phenomena are not fully understood, this finding implies that persisting pathophysiological processes are induced by hemicraniectomy and should be taken into consideration for surgical indications.