Hereditary isolated congenital ptosis is an autosomal dominant disorder with incomplete penetrance characterized by a variable degree of unilateral or bilateral drooping of the upper eyelids. We report linkage of this disorder in a large family to markers on chromosome 1p. In our sample of 37 meioses, nine informative markers did not recombine with the disease. D1S2677 gave a maximum two-point LOD score of 8.8 on the assumption of 90% penetrance (theta = 0). D1S447/2733 and D1S1616 flank the disease locus, with two-point LOD scores of 5.6/6.6 (theta = .04) and 4.9 (theta = .05), respectively, defining a region of 2.8 cM. FISH of YACs containing flanking recombinant markers localizes the gene to chromosome 1p32-p34.1. These data establish a map location for an isolated congenital ptosis gene and demonstrate that this disorder is genetically distinct from other extraocular muscle-specific disorders such as congenital fibrosis of the extraocular muscles and blepharophimosis.