Drooping of the upper eyelid (upper eyelid ptosis) may be minimal (1–2 mm), moderate (3–4 mm), or severe (>4 mm), covering the pupil entirely. Ptosis can affect one or both eyes. Ptosis can be present at birth (congenital) or develop later in life (acquired). Ptosis may be due to a myogenic, neurogenic, aponeurotic, mechanical or traumatic cause. Usually, ptosis occurs isolated, but may be associated with various other conditions, like immunological, degenerative, or hereditary disorders, tumors, or infections. Besides drooping, patients with ptosis complain about tired appearance, blurred vision, and increased tearing. Patients with significant ptosis may need to tilt their head back into a chin-up position, lift their eyelid with a finger, or raise their eyebrows. Continuous activation of the forehead and scalp muscles may additionally cause tension headache and eyestrain. If congenital ptosis is not corrected, amblyopia, leading to permanently poor vision, may develop. Patients with ptosis should be investigated clinically by an ophthalmologist and neurologist, for blood tests, X-rays, and CT/MRI scans of the brain, orbita, and thorax. Treatment of ptosis depends on age, etiology, whether one or both eyelids are involved, the severity of ptosis, the levator function, and presence of additional ophthalmologic or neurologic abnormalities. Generally, treatment of ptosis comprises a watch-and-wait policy, prosthesis, medication, or surgery. For minimal ptosis, Müller’s muscle conjunctival resection or the Fasanella Servat procedure are proposed. For moderate ptosis with a levator function of 5–10 mm, shortening of the levator palpebrae or levator muscle advancement are proposed. For severe ptosis with a levator function <5 mm, a brow/frontalis suspension is indicated. Risks of ptosis surgery infrequently include infection, bleeding, over- or undercorrection, and reduced vision. Immediately after surgery, there may be temporary difficulties in completely closing the eye. Although improvement of the lid height is usually achieved, the eyelids may not appear perfectly symmetrical. In rare cases, full eyelid movement does not return. In some cases, more than one operation is required.