A study of the histochemical staining of levator palpebrae superioris (LPS) was undertaken to measure the muscle fibre size in normal individuals and in patients with congenital dystrophic ptosis in order to see whether there is an alteration in muscle fibre size in congenital ptosis. Eight LPS specimens were obtained: 4 from normal patients (3 from normal levator divided in a bilateral brow suspension procedure and 1 from an exenteration specimen) and 4 from levator resection procedures for treatment of unilateral congenital ptosis. Cryostat sections from these specimens were stained histochemically to reveal muscle fibre types. The orthogonal diameters were measuring using a computer-generated program and the two groups compared using the Mann-Whitney mu-test. No statistically significant difference in muscle fibre diameter was found between normals and patients with congenital ptosis. There was also no change in the distribution or range of muscle fibre diameter in patients with congenital ptosis. Our findings do not support the classification of congenital ptosis as a dystrophy.