Behavioural or, in more general terms, problem analysis is usually regarded as the prerequisite of behaviour therapy. In behaviour therapy research, however, problem analysis does not play a key role. Patients are usually assigned to treatment methods on the basis of clinical diagnosis. It could be assumed that the lack of attention to the patient's individual characteristics should lead to poorer therapy outcome results. However, empirical data of a project reviewed in this paper in fact showed that assigning patients to standard treatment merely on the basis of clinical diagnoses provides results equal to or even better than those of optimized individual therapy strategies. Two premises of problem analysis were therefore tested. It could be shown that therapists would diagnose different problem conditions not only for patients with different types of phobia, but also, as expected, for patients with identical diagnoses. However, this did not—as would be expected according to the second premise of problem analysis—result in choosing different individual therapy strategies. One reason for these findings could be that behaviour therapy research has been able to provide treatment programs that have been differentiated and gradually optimized for specific diagnostic groups. To decide on the application of these treatment programs, clinical diagnoses are necessary. It is suggested that clinical diagnosis and problem analysis should be complementary. An integrative model is suggested.