The Yale Neuropsychoeducational Assessment Scales (YNPEAS) represent a newly developed tool designed to test the hypothesis that homogeneous subgroups of children with the more subtle neuropsychiatric disorders may be discerned and classified through shared historical, behavioral, familial, anatomic, neuromaturational, and biochemical characteristics. Consisting of a series of parent, physician, and school-related integrated assessment scales, the YNPEAS provide for the creation of a broad, multidimensional data base for each child. A major innovation of the YNPEAS is the provision of a mechanism for the orderly processing of the mass of clinical information into operational statements compatible with DSM-III constructs. This article presents the development of each of the component parts of the YNPEAS while also providing the historical perspective necessary to better comprehend the role of each of the scales. This instrument should be useful to both researcher and clinician as a tool with which to follow the natural history of a phenomenon; relate clinical dimensions across different diagnostic subgroups; and elucidate the genetic, social, and physiological interrelationships in the emergence or continuation of a disorder.