The effects of brief caffeine deprivation on vigilance performance, mood, and symptoms of caffeine withdrawal were studied in habitual coffee drinkers. Thirty male and female coffee drinkers were tested twice at midday (1130 to 1330 hours) after mornings in which they either consumed caffeinated beverages ad lib or abstained. Vigilance performance was tested with a 30-min computerized visual monitoring task. Mood and withdrawal symptom reports were collected by questionnaires. Caffeine deprivation was associated with impaired vigilance performance characterized by a reduction in the percentage of targets detected and an increase in response time, and by subjective reports of decreased vigor and increased fatigue and symptoms characterized by sleepiness, headache, and reduced ability to work. Even short periods of caffeine deprivation, equivalent in length to skipping regular morning coffee, can produce deficits in sustained attention and noticeable unpleasant caffeine-withdrawal symptoms in habitual coffee drinkers. Such symptoms may be a common side-effect of habitual caffeine consumption that contributes to the maintenance of this behavior.