Fetal alcohol syndrome (FAS) is a common developmental disorder with impairments in multiple neuropsychiatric spheres of varying severity. Few population-derived studies of the behavioral phenotype are available. The purpose of this study was to estimate the prevalence of neuropsychiatric disorders in three groups: subjects who met criteria for FAS (n=152); subjects who met criteria for partial FAS/ARND (n=150); and referred subjects who did not meet criteria for either FAS or partial FAS/ARND (n=86). Each subject had a standardized evaluation by a medical geneticist. All subjects were from North Dakota. We found increases in the prevalence rates of neuropsychiatric disorders in subjects with FAS compared to subjects with partial FAS/ARND and the lowest rates in the group that did not meet criteria for either FAS or partial FAS/ARND. Comorbid attention deficit hyperactivity disorder occurred in 73% of cases with FAS, in 72% cases with partial FAS/ARND, and in 36% subjects who did not meet criteria for either. For other neuropsychiatric disorders, a similar distribution of comorbidity was found. This study supports the concept of a continuum of impairment resulting from prenatal alcohol exposure. The presence of complex cognitive, behavioral, and physical symptomatology in the affected subjects with prenatal alcohol exposure would seem to fit well under the diagnostic rubric of fetal alcohol spectrum disorder (FASD). Diagnosis and long-term management will require increasing access to multidisciplinary child development teams including mental health professionals who treat children and adolescents. Adults will require care primarily from teams with expertise in mental health and developmental disabilities.