The word “ptosis,” an abbreviation for the term “blepharoptosis,” is used to describe the drooping of the upper eyelid. Ptosis may be congenital or acquired, and it may be unilateral or bilateral. It can occur in isolation or in syndromic form, and it is a feature of many conditions. Here, we discuss dominantly inherited congenital isolated ptosis. Work by Engle et al. (1997) on a pedigree with this condition, first described by Cohen (1972), has demonstrated linkage to markers in the region of 1p32-1p34.1 (MIM 178300) with a maximum two-point LOD score of 8.8. We describe the analysis of an independent large pedigree with dominant congenital isolated ptosis and linkage to the X chromosome.