Positron emission tomography (PET) using radiolabeled amino acids has shown great potential for more accurate diagnostics of cerebral gliomas. O-(2-[18F]Fluoroethyl)-L-tyrosine (FET) is a new tracer for PET which can be produced with high efficiency and distributed on a wide clinical scale in Germany. In a biopsy-controlled study, a significant improvement of the detection of true tumor extent of cerebral gliomas could be demonstrated by the combined use of FET PET and MRT in comparison with MRT alone. Advantages of FET PET are an improved guidance of biopsies, an improved planning of surgery and radiation therapy, and the differentiation of tumor recurrence from unspecific post-therapeutic tissue changes. Furthermore, FET PET appears to be particularly valuable in the prognosis of low-grade gliomas.