OBJECTIVE To determine the prevalence of lash ptosis (LP) in eyes with congenital and acquired blepharoptosis. METHODS We retrospectively graded photographs of 228 eyes from 174 patients with congenital or acquired blepharoptosis for LP. We used a 4-point rating scale for LP, in which 0 indicates no LP; 1, minimal; 2, moderate; and 3, severe. A prospective evaluation of LP in 30 eyes from 15 patients without blepharoptosis (control eyes) was also performed. RESULTS A total of 107 eyes (in 87 patients) demonstrated congenital blepharoptosis and 121 eyes (in 87 patients) had acquired blepharoptosis. A moderate to severe rating of LP (rating, >/= 2) occurred in 60.7% of eyes with congenital blepharoptosis, 28.9% of eyes with acquired blepharoptosis, and 6.7% of control eyes. Lash ptosis (rating, >/= 1) was present in 91.6% of eyes with congenital blepharoptosis, 83.5% of eyes with acquired blepharoptosis, and 33.3% of control eyes. The mean LP rating was 2.1 for eyes with congenital blepharoptosis, 1.3 for eyes with acquired blepharoptosis, and 0.6 for control eyes. CONCLUSIONS Lash ptosis was common in the patients with blepharoptosis. Moderate to severe LP occurred more commonly in all forms of blepharoptosis compared with normal eyes, with more frequent and more severe LP demonstrated in eyes with congenital blepharoptosis.