It has been estimated that 22 - 32% of people with mental retardation or learning disability have co-existing epilepsy. Despite such high prevalence and although there may be particular concerns over the effects of treatment on behaviour and cognition in this population, few studies have specifically addressed these concerns. Topiramate (TPM) is one of the modern antiepileptic drugs that has been approved for the treatment of a broad range of seizure types in both children and adults. There is evidence of associated improvement in behaviour with treatment but data is conflicting. The investigators aim to further study the effect of TPM on seizure control and behaviour using the Scales of Independent Behavior-Revised (SIB-R) which has been applied in similar patient populations and is widely adopted locally to assess the behaviour of people with mental retardation. This is a naturalistic, open label, single arm prospective study of 16-week in duration. Eligible adult patients will be initiated on TPM. Patients will be evaluated at baseline, end of weeks 4, 10 and 16. At each visit seizure control and any adverse events will be assessed. Behaviour will be assessed using SIB-R (Chinese version) at baseline and each study visit. At the end of the study period the patient's overall improvement will be rated by the investigator and the caregiver using global evaluation scales. Patients with improvement will be maintained on TPM after the end of the study period Titration schedule Topiramate will be administered orally as per usual clinical practice. Treatment will be initiated at 25 mg daily for 1 week, and increased in 25- to 50-mg increments at one- to two-weekly intervals, to an initial target dose of 100 - 200 mg daily in 2 divided doses according to each individual's response. Further dose adjustment can be made in response to further seizures or emergence of adverse events..