Abstract Caffeine is a widely ingested and generally beneficial drug. However, when taken in excess, anxiety related symptoms become increasingly apparent. A case of caffeinism, which presented as a paranoid delusion, is reported as an extreme example of this. A study of 60 hospital inpatients revealed that about 40% of them consumed sufficient caffeine to produce symptoms of caffeinism. It is thus recommended that all patients should be questioned on their caffeine intake. Also, caffeinism should be considered as a differential diagnosis of anxiety states.