Caffeine affects most physiological systems. Few studies have attempted to document which somatic symptoms are commonly associated with caffeinism. To answer this question, 124 general hospital patients were evaluated and reported somatic symptoms among low, moderate and high caffeine users were compared. Diuresis, insomnia, withdrawal headache, diarrhea, anxiety, tachycardia and tremulousness were most commonly reported, in descending order of frequency. Differences among high, moderate and low users were common and some dose-response associations were apparent. Most symptoms were explainable by caffeine''s known CNS neuropharmacological effects or peripheral pharmacological actions.