This work contributes to outsourcing research by shedding some light on IT outsourcing relationships. A theoretical model is developed that shows the influence of determinants on relationship quality. Relationship quality is captured by a set of five dimensions from previous literature and enhanced by two new dimensions (communication quality, forbearance). Determinants from the literature are extended by two new elements (interaction structure, service quality). By using a case study approach from the German financial industry, we show the applicability of interaction structures and service quality as relationship quality determinants. Interaction structures like employee trainings or transfer of staff have a strong positive impact on communication quality and mutual business understanding, whereas service quality mainly influences the level of conflict in a relationship. The results regarding the two proposed relationship quality dimensions are mixed. Communication quality is a good measure for capturing relationship quality and shows strong connections to interaction intensity and interactions structures. The applicability of forbearance as a relationship quality dimension is ambiguous. Some banks see forbearance as dimension of relationship quality, while others use forbearance as a strategic element to force the provider into delivering additional or better services.