Until recently, only nuclear medicine techniques allowed combining whole-body anatomical and functional information. Now, diffusion-weighted imaging seeks to compete with these techniques in the field of oncology, providing assessment of tumour spread, characterizing lesions and evaluating therapeutic response. The first issue has been widely evaluated since the first published whole-body diffusion-weighted images looking like scintigraphy. Optimal background suppression and diffusion weighting highlighted tumours with restricted diffusion. For the two latter issues, ADC seems to represent the key element; it should allow differentiation between benign and malignant tissue, and active from inactive lesions after treatment. This is of paramount importance for the monitoring of lymphomas treated with chemotherapy alone, or for solid tumors treated by neoadjuvant therapies. However, imaging protocols still differ between studies, and there is considerable overlap in ADC values between healthy and neoplastic tissues. Despite this difficulty to identify a clinically reliable threshold for malignancy, there is no doubt that ADC will represent as a reliable biomarker in the future for some malignancies, and lymphomas represent a helpful model for this purpose.