Sodium valproate is an established antiepileptic drug used against a broad range of seizure types. Lamotrigine, a newer antiepileptic drug available since late 1980s, has a similar range of action and is approved as first-line treatment for epilepsy in the United States and many European countries as well as in Hong Kong. Recently, concern has been raised over the association between valproate treatment and polycystic ovarian syndrome, a condition characterised by multiple cysts in the ovaries in women and a range of hormonal and metabolic disturbances. Cross-sectional studies from Finland suggest that up to 40% of women treated with valproate have polycystic ovaries. Lamotrigine substitution for valproate has been reported to normalise these parameters in some patients. Elevated serum insulin and androgen levels have also been reported in over 50% of male patients taking valproate for epilepsy. However, such high incidence of hormonal abnormalities associated with valproate treatment has not been reproduced in studies conducted in other western populations. No similar studies in Chinese patients have been reported. In addition, these cross-sectional studies suffer from many potential confounding factors, such as previous treatment with other antiepileptic drugs, variation in duration of treatment, thus limiting the ability to establish a causal relationship.