Growing knowledge of the molecular mechanisms of oncological disease plays a key role in the improvement of prevention, diagnosis and treatment of malignant tumors. In this review, positron emission tomography (PET) is described as a mediator between molecular oncological research and clinical management of tumor patients. The most promising applications of PET in the near future include tumor imaging with newly developed tracers for diagnosis, staging and grading purposes, therapy monitoring with proliferation and apoptosis markers and definition of the tumor environment (e.g. hypoxia, neoangiogenesis) prior to therapy. Many of these applications will greatly benefit from the use of integrated PET/CT due to its precise spatial and morphological assignment of functional information. In conclusion, PET is both capable and necessary for the transference of new biological knowledge to clinical practice. Thus, PET constitutes a strong basis for an advanced and individually tailored approach to tumor patients.