Recent investigations of caffeine abuse have questioned the indiscriminant use of this commonly accepted drug. In some individuals, chronic excessive caffeine consumption leads to the development of caffeinism, a syndrome which includes increased anxiety, depression, frequency of psychophysiological disorders, and possibly degraded performance. This paper reviews research demonstrating the abuse potential of caffeine. Special attention has been given those factors which mediate the wide individual differences in consumption patterns, susceptibility to abuse, and the varied psychological and physiological responses to this drug. While the development of caffeine abuse is probably best viewed as an idiosyncratic process, general guidelines for the recognition of potential abuse, and caffeinism proper, are offered.