Many of the most important choices in people's lives have an inter-temporal dimension, i.e., these choices are associated with a flow of benefits or costs that accrue in the future. In addition, such choices are frequently habit- forming. Yet, little is known about habit-forming inter-temporal choice behavior. This paper reports the results of an inter-temporal choice experiment with habit-formation. Subjects' choices deviate systematically from individually optimal decisions in the direction of over consumption. This over- consumption is partly driven by loss avoidance, comparable to a real life situation in which addicted people consume addictive substances only in order to overpower withdrawal symptoms. Our results thus reject the theory of rational addiction.