The study of habit acquisition and expression is considered relevant to improve our understanding of mental disorders characterised by the presence of compulsive or incontrollable behaviours. Most studies on habit learning, both in animals and in humans, are based on positive reinforcement paradigms. However, the compulsions and habits involved in some mental disorders may be better understood as avoidance behaviours, which involve some peculiarities such as anxiety states that have been shown to promote habitual responses. Consequently, we studied habit acquisition by using a free-operant discriminated avoidance procedure. Participants learned to avoid an aversive noise presented either to the right or to the left ear by pressing two different keys. After a devaluation phase where participants could reduce the volume of the noise presented to one of the ears, participants went through a test phase identical to the avoidance learning phase except for the fact that the noise was never administered. Habit acquisition was inferred by comparing the rate of responses to the stimulus signalling the devalued reinforcer and to the stimulus signalling the non-devalued reinforcer. Habitual responses would entail the absence of differences between the referred conditions. Finally, we discuss the theoretical and clinical implications of the results obtained.