Vocational interest inventories are commonly analyzed using a unidimensional approach, that is, each subscale is analyzed separately. However, the theories on which these inventories are based often postulate specific relationships between the interest traits. This article presents a multidimensional approach to the analysis of vocational interest data, which takes these relationships into account. Models in the framework of Multidimensional Item Response Theory (MIRT) are explained and applied to a widely used German vocational interest inventory based on the RIASEC model, the AIST-R. MIRT models were more appropriate to describe the data than unidimensional models. It follows that responses to some items were not only influenced by the interest type they were designed to measure but also by another dimension. The advantages of MIRT models are discussed.