Impaired attention is a frequently reported side effect of anti-epileptic medication, as well as a frequent general complaint of epilepsy. It is thus important to evaluate the effect of new medications on attention processes. Attention was assessed weekly in ten subjects receiving topiramate over a 3 month period. Attention was evaluated with digit span, a widely used index of attention. Different number sequences were constructed and randomized to allow for repeated use. Four of nine subjects showed significant correlations between topiramate dosage and forward digit span measured weekly, such that higher dosage was associated with poorer attention. The average topiramate dosage and seizure reduction did not differ between these subjects and those who did not show a significant relationship.