Double-blind, Placebo-controlled Study of Levetiracetam in Adults With POS

Inclusion Criteria: 1. subject suffering from partial onset seizures, whether or not secondarily generalized, 2. presence of the following during the eight weeks of the historical baseline period: at least eight partial seizures (type IA, IB or IC) with or without secondary generalization. 3. subject on a stable dose of at least one and no more than two other concomitant antiepileptic drugs (AEDs). 4. subject who has been exposed to at least one classical AEDs, 5. CT scan or MRI performed within the last 2 years and free of neoplasia, progressive cerebral disease or any other progressively neurodegenerative disease. Exclusion Criteria: 1. history of status epilepticus within three months prior to the Selection visit, 2. subjects whose seizures cannot reliably be counted on a regular basis due to their fast and repetitive occurrence (clusters or flurries), 3. use of any medication (other than the concomitant AED) that influences the central nervous system (CNS) unless on a stable regimen for at least 1 month prior to the Selection visit. Antidepressants (except amitriptyline, mianserin and fluoxetine), anxiolytics and hypnotics are allowed. Intermittent benzodiazepines are allowed as long as the frequency is not greater than one single administration per week for at least 3 months prior to the Selection visit. Neuroleptics and Traditional Chinese AEDs are not allowed., 4. history or presence of pseudoseizures,