The author reports that high intake of caffeine ("caffeinism") can produce symptoms that are indistinguishable from those of anxiety neurosis, such as nervouness, irritability, tremulousness, occasional muscle twitchings, insomnia, sensory disturbances, tachypnea, palpitations, flushing, arrhythmias, diuresis, and gastrointestinal disturbances. The caffeine withdrawal syndrome and the headache associated with it may also mimic anxiety. Patients with caffeinism will generally be identified only by routine inquiry into their caffeine intake. The psychiatrist should especially suspect caffeinism in patients who do not respond to psychopharmacological agents or who have psychophysiological complaints and recurrent headaches, chronic coffee-drinking patients on inpatient psychiatric services, and "hyperkinetic" children. Three case reports illustrate the syndrome.