Imaging biomarkers have a potential to depict the hallmarks of cancers that characterise cancer cells as compared to normal cells. One pertinent example is 3'-deoxy-3'-(18)F-fluorothymidine positron emission tomography ([(18)F]FLT-PET), which allows non-invasive in vivo assessment of tumour proliferation. Most importantly, [(18)F]FLT does not seem to be accumulating in inflammatory processes, as seen in [(18)F]-fludeoxyglucose, the most commonly used PET tracer for assessment of cell metabolism. [(18)F]FLT could therefore provide additional information about the tumour biology before, during and after treatment. This systematic review focuses on the use of [(18)F]FLT-PET tumour uptake values as a measure of tumour response to therapeutic interventions. The clinical studies which evaluated the role of [(18)F]FLT-PET as a measure of tumour response to treatment are summarised and the evidence linking [(18)F]FLT-PET tumour uptake values with clinical outcome is evaluated.