Over the last years, it has been shown that novel imaging technologies rapidly change the working environment of radiologists, nuclear medicine physicians, and oncologists. Positron emission tomography/magnetic resonance imaging (PET/MRI) as a new hybrid modality in clinical environment combines functional and molecular imaging and provides multiparametric tissue information simultaneously. Both, PET and MRI are evolving continuously and have separately become an essential part of oncologic imaging. Thus, it is expected that the combination will lead to further insights and improvements in initial diagnoses, therapy monitoring, and the assessment of therapy response. In this work-in-progress review article, we give a short technical introduction to PET/MRI, summarize the current state in research of PET and MRI in selected oncologic diseases and give an overview of the progress that has been achieved so far with integrated PET/MRI-systems, underlined by the experiences in our own department.