Numerous systemic drugs produce adverse effects that involve the eye. Pigmentary inclusions of the lids or conjunctivae or both may be caused by a variety of drugs, including amiodarone, chlorpromazine, and gold salts, while conjunctivitis and blepharoconjunctivitis have been associated with isotretinoin, sulfonamides, salicylates, and antineoplastic agents. Dry eye complaints may be caused by antihistamines, beta-receptor blocking agents prescribed for cardiovascular problems, antianxiety agents, and tricyclic antidepressants. Several drugs have been well documented as causes of keratopathies and/or lenticular deposits, including chloroquine and hydroxychloroquine, chlorpromazine, gold salts, systemic corticosteroids, nonsteroidal antiinflammatory drugs, and the antiarrhythmic agent amiodarone. Visual acuity may be decreased by transient changes in refractive error caused by sulfonamides, the antifungal agent metronidazole, thiazide diuretics, and carbonic anhydrase inhibitors. Dilation of the pupil may be caused by anticholinergic drugs, antihistamines, antidepressant agents, and central nervous system stimulants such as cocaine, methylphenidate, and amphetamines. Nystagmus, diplopia, and extraocular muscle palsies have been associated with central nervous system depressants, antihistamines, barbiturates, and elevated blood ethanol concentrations. Intraocular pressure can be elevated in susceptible individuals by long-term use of topical or systemic corticosteroids. Numerous drugs have been associated with retinal toxicity, including chloroquine and hydroxychloroquine, thioridazine, tamoxifen, and talc, which may embolize to the retinal circulation when administered by long-term drug abusers. The antituberculosis agents ethambutol and isoniazid have been implicated as causes of reduced acuity, visual field defects, and disturbances of color vision. Optic neuritis and retrobulbar neuritis may result from the use of chloramphenicol. This paper describes these and other adverse ocular effects that may be encountered when examining patients who are taking systemic drugs.