Metabolic imaging and early response assessment by positron emission tomography (PET) are gaining importance in guiding treatment of localised and metastatic gastrointestinal tumours. During a workshop organised by the European Organisation of Research and Treatment of Cancer (EORTC) Gastrointestinal Tract Cancer Group the most relevant research questions, methodological aspects and unmet clinical needs in this disease were discussed. Potential future trials were drafted. This paper reviews the lectures and discussions held during this workshop and summarises the action points for the further investigation of metabolic imaging to guide treatment in gastrointestinal tumours.