A postal survey showed that the majority of 49 leading international neurologists involved with multiple sclerosis research felt that currently existing outcome measures for this illness were inadequate, and that there was a need for a new measure which should be patient orientated, multidimensional, and not biased towards any particular disability. The Guy's Neurological Disability Scale (GNDS) was subsequently devised as a simple and user-friendly clinical disability scale capable of embracing the whole range of disabilities which could be encountered in the course of multiple sclerosis. It has 12 separate categories which include cognition, mood, vision, speech, swallowing, upper limb function, lower limb function, bladder function, bowel function, sexual function, fatigue, and 'others'. The GNDS was found to be acceptable to neurologists and patients, reliable, responsive, and valid as a measure of disability. The scale was also found to be valid when applied by non-neurologists, over the phone, or via a postal questionnaire.