Involutional ectropion and entropion are characterized by excessive horizontal eyelid length, which is thought to be secondary to laxity of the medial and lateral canthal tendons and to the stretching of the tarsus. Histopathological features of the surgical eyelid specimens from patients with involutional ectropion and entropion were evaluated.Prospective histopathological study.Eighteen full-thickness eyelid specimens from patients with involutional ectropion and entropion were obtained during horizontal eyelid shortening procedures performed at the Ministry of Health Ankara Training and Research Hospital.All specimens were fixed in 4% formaldehyde solution and sectioned sagittally. Hematoxylin-eosin, periodic acid-Schiff, and Masson's trichrome staining were done for all specimens. Histopathologic alterations of the tarsal plate, the palpebral portion of the orbicularis muscle, and the conjunctiva were examined.The patients ranged in age from 60 to 80 years. The main histopathologic features of the ectropic eyelids included collagen degeneration and elastosis of the tarsal plate, increased amounts of adipose tissue in the distal tarsus, and subacute inflammation and epidermalization of the tarsal conjunctiva. Specimens from patients with involutional entropion generally had milder degrees of these histopathological features.The causes of the excessive horizontal length of the eyelid, which is thought to be secondary to laxity of the medial and lateral canthal tendons, may be collagen degeneration and elastosis of the tarsal plate and canthal tendons.