Improvements of radionuclide and magnetic resonance-based imaging modalities over the past decade have enabled clinicians to noninvasively assess the dynamics of disease-specific processes at the molecular level in humans. This article will provide an overview of the recent advances in multimodal molecular neuroimaging in patients with primary brain tumors. To date, a range of complementary imaging parameters have been established in the diagnosis of brain tumors. Magnetic resonance imaging (MRI) provides mostly morphological and functional information such as tumor localization, vascular permeability, cell density, and tumor perfusion. The use of positron emission tomography (PET) enables the assessment of molecular processes, such as glucose consumption, expression of nucleoside and amino acid transporters, as well as alterations of DNA and protein synthesis. Taken together, MRI and PET give complementary information about tumor biology and activity, providing an improved understanding about the kinetics of tumor growth.