Background: Most patients with pure nonprogressive congenital cerebellar atax ia have a sporadic form of unknown heredity and etiology. Several small families have been reported with a dominantly inherited nonprogressive congenital ataxia (NPCA). Methods: The authors ascertained and clinically characterized a four-generati on pedigree segregating an autosomal dominant type of congenital nonprogressive cerebellar ataxia associated with cognitive impairment. Following the exclusion of several SCA localizations (SCA-1,2,3, 4,5, 6,7,8, 10, 12, 17, IOSCA, and DR PLA), a genome-wide linkage study was performed. Results: Examination of the f amily showed that all affected members had gait ataxia and cognitive disability with variable features of dysarthria, dysmetria, dysdiadochokinesia, nystagmus, dystonic movements, and cerebellar hypoplasia on imaging. Clinical signs of pyra midal tract dysfunction and sensory changes were absent. A genome-wide search in this family detected linkage to chromosome 3p with a maximum two-point lod score of 4.26 at D3S3630. This localization to the pter is distal to D3S1304, as defined by a recombination event. This overlaps with the SCA15 locus, with the critical overlapping region between the microsatellite markers, D3S1304 and D3S1 620 (approximately 8 cM). Conclusion: Autosomal dominant congenital nonprogressi ve cerebellar ataxia with or without cerebellar hypoplasia overlaps with the SCA 15 locus on chromosome 3pter. Background: Most patients with pure nonprogressive congenital cerebellar atax ia have a sporadic form of unknown heredity and etiology. Several small families have been reported with a dominantly inherited nonprogressive congenital ataxia (NPCA). Methods: The authors ascertained and clinically characterized a four-generati on pedigree segregating an autosomal dominant type of congenital nonprogressive cerebellar ataxia associated with cognitive impairment. Following the exclusion of several SCA localizations (SCA-1,2,3,4,5,6,7,8,10,10,12, IOSCA , and DR PLA), a genome-wide linkage study was performed. Results: Examination of the f amily showed that all affected members had gait ataxia and cognitive disability with variable features of dysarthria, dysmetria, dysdiadochokinesia, nystagmus, dystonic movements, and cerebellar hypoplasia on imaging. Clinical signs of pyra midal tract dysfunction and sensory changes were absent. A genome-wide search in this family detected linkage to chr This localization to the pter is distal to D3S1 304, as defined by a recombination event. This overlaps with the SCA15 locus, with the critical overlapping region between the microsatellite markers, D3S1304 and D3S1 620 (approximately 8 cM). Conclusion: Autosomal dominant congenital nonprogressi ve cerebellar ataxia with or without cerebellar hypoplasia overlaps with the SCA 15 locus on chromosome 3pter.