This brief review considers to what extent Magnetic Resonance Spectroscopy (MRS) can play a role in monitoring early tumour response with examples of preclinical studies and selected clinical studies in tumours of children and young adults. An early non-invasive indicator of tumour response to therapy would provide useful information regarding the effectiveness of therapy. This might be a relevant prognostic factor in new patients and in phase II studies could facilitate recommendations at an early stage as to whether to continue treatment. This review suggests that several markers and ratios are emerging as potential prognostic markers, but larger prospective studies are needed before translating this into clinical practice.