The aim of the study was to investigate what factors the physiotherapy experts in psychiatric physiotherapy believed to be important in the interaction between the patient and the physiotherapist (PT). The objective was to obtain a deeper insight into their reasoning concerning interaction and treatment outcomes. Eleven nominated 'expert' PTs were each interviewed twice. Triangulation of important events, an exemplar (critical incident) and a key informant interview were used in the data collection. A qualitative design with crosscase analysis was used in the data analysis. Important interaction factors were divided into a 'prerequisites dimension', 'interaction dimension' and 'outcome dimension'. In the prerequisites dimension there were three themes: 'prerequisites of the PT', 'prerequisites of the patient' and 'external factors'. In the interaction dimension there were also three themes: 'ways of contact', 'therapeutic process' and 'structure of treatment'. In the outcome dimension the theme 'outcome' and the two categories 'patient - awareness of own resources and 'PT - improvement of interaction skills with the aid of reflection' were found. Interaction was considered to be important for the outcome and for the patient's awareness of his/her resources. The body awareness skills of the PT, the therapeutic relationships, help for the patient to identify his/her resources and the contract were also important. The ability to be fully mentally present in the encounter and the use of non-verbal skills were emphasized. Supervision and reflection about the outcome increased the PT's interaction skills in a learning process. The physiotherapy process expressed was resource-oriented.