This study aimed to describe the Tree Theme Method (TTM) as a method for intervention in psychosocial occupational therapy. The TTM is based on theories concerning creative activities and occupational storytelling and story making. In order to exemplify the method a case study of a treatment process with follow up was undertaken. The participant was a female client suffering from anxiety and depression. During an interview the client painted symbolic trees on five different occasions with specific variations of the tree theme: a tree symbolizing her present life, her childhood, adolescence, adulthood, and, finally, a tree representing her future. The trees were used as starting points for the client to tell her life story. The intention was that she would find new strategies for how to change her daily life. Three years later there was a follow up stage where the client painted new trees and told her story. Some life themes were identified. The TTM appears suitable for intervention in psychosocial occupational therapy. In future studies the TTM should be subjected to evaluation research based on several clients in order to develop a deeper understanding of the process and what kind of results changes in the TTM intervention may provide.