Aim. This single-case study investigated adaptive shifts in behaviour observed in the early stage of a successful course of Affect Phobia Therapy (APT), a form of Short Term Dynamic Psychotherapy (STDP) with the goal to discover whether early gains could be made by a patient presenting with anxiety, relationship difficulties, and low self-worth, and what mechanisms of change would facilitate these gains. Methods. Eight early sessions were rated using the Achievement of Therapeutic Objectives Scale (ATOS), which measures the extent of beneficial effects of therapy achieved by the patient. Patient symptoms and functioning was assessed using the Symptoms Checklist 90 Revised (SCL-90-R), the Inventory of Interpersonal Problems (IIP) and the Rosenberg Self-Esteem Scale (RSE). It was hypothesized that exposure to conflicted feelings would lead to desensitization (i.e., the conflicted feeling being tolerated with reduced levels of anxiety or shame). Results. Results confirm that desensitization did occur and strong improvement was noted by session 10 on all measures. Conclusions. Findings suggest that significant changes can occur early in therapy and the key mechanisms of change are exposure to warded off feelings and lowering of inhibition. These findings are of interest in light of the current trend towards brief therapies and the search for mechanisms of change.