Electronic cigarettes are becoming increasingly popular and therefore psychiatrists are being confronted more and more frequently by this relatively new phenomenon. We discuss the case of a patient who switched from traditional cigarettes to electronic cigarettes and thereupon had a significant increase in the clozapine serum level. The increased level led to considerable side-effects and, as a result, the patients clozapine dosage had to be reduced. In theory, a rise in the clozapine serum level is to be expected after such a switch. However, since electronic cigarettes have not been on the market for very long, psychiatrists need to be aware of the risks and dangers that can arise as a result of exceptionally high clozapine levels.