A Placebo-controlled Study to Investigate Safety and Efficacy of BIA 2-093

Inclusion Criteria: * Male and female patients aged 18-65 years * Patients with simple or complex partial seizures with or without secondary generalization since at least one year prior to randomisation visit * At least 4 seizures per month within the last 2 months prior to randomisation * Stable dose regimen of a maximum of two of the following AEDs: phenytoin, valproate, primidone, phenobarbital, lamotrigine, gabapentin, topiramate, clonazepam, during 2 months prior to randomisation * Electroencephalogram (EEG) findings not contradicting the epilepsy diagnosis (e.g., primarily generalized epilepsy) * Written informed consent. Exclusion Criteria: * Patient with nervus vagus stimulation * Patient with primarily generalized seizures * Known progressive neurological disturbance * A history of status epilepticus within the past 3 months * Seizure of non-epileptic origin * Restricted legal competence and incapability to follow trial instructions * Major psychiatric disorders * Concurrent drug therapy with monoamine oxidase inhibitors or calcium channel blockers * Need of excluded concomitant medication (see section 9.4.6.2) * Use of oxcarbazepine or carbamazepine during the last 6 months before the randomisation visit * Known hypersensitivity to oxcarbazepine or carbamazepine, or its metabolites * Abuse of alcohol, drugs or medications * History of relevant cardiac, renal, hepatic, endocrine, gastrointestinal, metabolic, hematologic or oncology disorders * Second- or third-degree atrioventricular block not corrected with a pacemaker * Relevant laboratory abnormalities (e.g., Na+\< 130 mmol/L, alanine (ALT) or aspartate (AST) transaminase \>2.0 times the upper limit of normal, white blood cell (WBC) count \<3000 cells/mm3) * Pregnancy, nursing or inadequate contraception in women of childbearing age (oral contraception should be combined with a barrier method) * Participation in other clinical trials within the last 2 months * History of non-compliance.