The efficacy of an antiepileptic drug (AED) is determined at present by the drug-elicited reduction in seizure frequency. Reduction of seizure frequency as the sole measure of efficacy does not account for treatment-induced reductions in seizure severity and positive psychological effects experienced by the patient. A clinical trial was undertaken in which seizure frequency was the primary and seizure severity and psychological well-being were the secondary measures of efficacy. Psychological assessment and seizure frequency were monitored in patients whose epilepsy was treated with lamotrigine (LTG) or placebo. The results indicate that LTG is an effective AED, causing reductions in seizure frequency and severity and improvements in mood and mastery. In addition, the study demonstrated that the use of seizure severity scales, especially the ictal subscale, may enhance the sensitivity of assessment of trials of AED treatments.