The Sleep Disorders Questionnaire (SDQ) is a 176-item questionnaire designed to diagnose the presence of common sleep disorders. This study set out to assess the validity of a Dutch translation of the SDQ. Scores on 145 questionnaires were analyzed. A cluster analysis of these scores revealed the following clusters: healthy, depression, insomnia, narcolepsy, and apnea. The cluster classification proved correct for 67% of the subjects, as determined on the basis of polysomnography. These results show that the Dutch SDQ is a reasonably valid instrument for diagnosing sleep disorders.