Positron emission tomography (PET)/computerised tomography (CT) has proved useful in a number of haematological malignancies, particularly in Hodgkin lymphoma (HL) and aggressive non-Hodgkin lymphomas (NHL). It is recommended in the staging of HL and aggressive NHL, it has been shown to be prognostically important early during treatment, and it has been incorporated in the response criteria. However, treatment modification based on early scans is still experimental, and routine use in follow up cannot be recommended. The use of PET/CT in other lymphoma types and other haematological malignancies is still under evaluation.