Quantitative assessment of seizure severity has been approached using a variety of systems. This review describes currently available methods and possible new approaches to seizure assessment for clinical trials. A review of the literature on methods of seizure assessments resulted in tabulation of the seizure rating scales known as VA, Chalfont-National Hospital, Liverpool, Hague, and the Occupational Hazard Scale. Seizures have been evaluated by simply counting all events, counting events by type, by clinician ratings, patient ratings, and combinations. Each of the scales has advantages and disadvantages. Most scales share core components: seizure frequency, seizure type, seizure duration, postictal events, postictal duration, automatisms, seizure clusters, known patterns, warnings, tongue biting, incontinence, injuries, and functional impairment. This review revealed a partial consensus about aspects of seizures that are important markers for severity. However, usefulness of the existing scales is limited by lack of data on responsiveness. New approaches are needed to assess changes in seizure severity as a result of an intervention in a clinical trial.