The DEPTh project is a randomized controlled trial comparing the effectiveness of cognitive behaviour therapy (CBT) and person-centered therapy for the prevention of psychosis among young people who are at ultrahigh risk. It is being conducted on two sites in New South Wales: the Hunter Valley and the Greater Western Area. The CBT is modeled on the manual developed by Paul French and Tony Morrison in the UK. This form of CBT has been shown in one trial to be effective in preventing transition to psychosis. However, it does not include any techniques that specifically focus on the reduction of substance abuse even though such abuse, especially of cannabis, is known to be very high among people who are at ultrahigh risk, and cannabis use has been found in prospective studies to be associated with the later onset of psychosis. Therefore, we have adapted French and Morrison's CBT by integrating it with a manual for motivational interviewing (MI) with young cannabis users. MI is directed toward the resolution of ambivalence and movement toward change, with the resources and motivation to change considered to reside within the client. The therapist's task is to create a set of conditions that will enhance the client's own motivation and commitment for change by drawing on their personal perceptions, goals and values. The ways in which CBT and MI are integrated in the DEPTh project will be illustrated with case material.