BACKGROUND: Existing research has suggested that there can be potential drug-drug interaction (DDI) between antiepileptic drugs (AED) and anticancer drugs (ACD). However, information on the prevalence of patients on concurrent oral AED and oral ACD is limited. METHODS: A retrospective study was conducted at the National Cancer Centre Singapore. Prevalence was calculated by identifying prescriptions with both oral AED and oral ACD from the outpatient prescription database over three years. Prevalence and physicians' prescribing patterns were evaluated. Co-prescription was defined as medications that were prescribed by the same physician on the same day. Potentially interacting combinations were further detected using an existing database, OncoRx (www.onco-informatics.com). RESULTS: 42,810 prescriptions that contained at least one oral ACD were identified from the database. The number and prevalence of prescriptions that had a combination of oral ACD and AED were 274 and 0.64%, respectively, with the majority (82.8%) of the AED-oral ACD pairs being co-prescribed. Per patient, the average number of exposure days to the AED-oral ACD pair was 19.5 days annually. Fifty-one (18.6%) prescriptions were identified as containing potentially interacting AED-oral ACD pairs. DISCUSSION: There is a relatively low prevalence of AED-oral ACD combined exposure in the population we sampled; however, the combined exposure is long enough to produce clinically important DDI effects.