The anticonvulsant hypersensitivity syndrome is a rare, potentially fatal entity, which incidence varies of 1:1.000 to 1:10.000 expositions to fenitoin, carbamazepine or fenobarbital. This syndrome occurs due to epoxi-hidrolase deficiency, an enzyme involved in metabolization of these drugs. We report two cases with clinical and laboratories features of this syndrome. It is important to recognize this syndrome because can occur fatal systemic.