The aim of the current study was to assess the ability of PET imaging agents to detect early response to therapy in an orthotopic experimental rodent model of glioma. Clinically, MRI and [(18)F]FDG PET are routinely used but their ability to assess early therapeutic response can be limited. In this study, nude rats were implanted with U87-MG tumors orthotopically and imaged with either [(18)F]FDG or [(18)F]FLT to determine which tracer acts as the most sensitive biomarker for evaluation of treatment response in animals undergoing anti-angiogenic therapy with sunitinib, a receptor tyrosine kinase (RTK) inhibitor. Of the radiopharmaceuticals tested, [(18)F]FLT proved to be the most sensitive biomarker in the proliferating glioma, based on tumour-to-normal tissue radiotracer uptake (TNR ~17) in comparison to [(18)F]FDG (TNR ~1.7). Furthermore, [(18)F]FLT displayed earlier assessment of therapy efficacy, than either tumour volume measured by MRI or [(18)F]FDG PET imaging. Overall, longitudinal molecular imaging with [(18)F]FLT provides earlier detection of therapy response than either of the commonly used clinical imaging modalities potentially improving patient management.