Restless legs syndrome is a common yet frequently undiagnosed sensorimotor disorder. In 1995, the International Restless Legs Syndrome Study Group developed standardized criteria for the diagnosis of restless legs syndrome. Since that time, additional scientific scrutiny and clinical experience have led to a better understanding of the condition. Modification of the criteria is now necessary to better reflect that increased body of knowledge, as well as to clarify slight confusion with the wording of the original criteria. The restless legs syndrome diagnostic criteria and epidemiology workshop at the National Institutes of Health. Members of the International Restless Legs Syndrome Study Group and authorities on epidemiology and the design of questionnaires and scales. To modify the current criteria for the diagnosis of restless legs syndrome, to develop new criteria for the diagnosis of restless legs syndrome in the cognitively impaired elderly and in children, to create standardized criteria for the identification of augmentation, and to establish consistent questions for use in epidemiology studies. The essential diagnostic criteria for restless legs syndrome were developed and approved by workshop participants and the executive committee of the International Restless Legs Syndrome Study Group. Criteria were also developed and approved for the additional aforementioned groups.