Interpretation of studies from all imaging modalities requires a knowledge of the possible pitfalls that may occur due to normal variation, artefacts and processes which may mimic pathology. The applications and use of not only 18-fluoro-2-deoxyglucose but also l-[methyl-(11)C] methionine positron emission tomography (PET) are widening and it is timely that the currently recognised interpretative pitfalls are reviewed as the number of dedicated PET scanners and coincidence gamma cameras increases.