OBJECTIVE: The authors review the usefulness, reliability, and validity of recently proposed subtypes of primary insomnia. DSM-III uses "primary insomnia" to indicate chronic insomnia not associated with other diagnosable mental or medical disorders, whereas the International Classification of Sleep Disorders (ICSD) recognizes three subtypes: psychophysiological insomnia, idiopathic insomnia, and sleep state misperception. METHOD: After reviewing all of the primary source references for each insomnia disorder in the ICSD and all of the additional primary sources cited in each of these, the authors conducted an automated literature search using Medline. Of the 48 primary sources located, the authors selected 27 studies that were reported in peer-reviewed journals, had the largest available subject groups, used diagnostic reliability procedures, and included control groups. RESULTS: The studies reviewed contained limited empirical support for the proposed distinction between idiopathic and psychophysiological insomnia. Sleep state misperception appears, however, to be a highly prevalent feature of chronic insomnia generally, rather than only a specific disorder per se. CONCLUSIONS: The authors conclude that there is not yet sufficient empirical evidence to warrant the abandonment of DSM-III-R "primary insomnia" and the adoption of the ICSD subtypes in DSM-IV. However, they affirm the heuristic value of the ICSD subtypes and the need for field trials to compare the performance characteristics of the DSM-III-R and ICSD systems with respect to 1) interrater reliability, 2) effects of rater expertise (generalist versus specialist) on rates of agreement, and 3) effects of polysomnographic data on rates of agreement.Abstract Teaser