The aim of this review was to determine the usefulness of diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) in the assessment of head and neck tumors. DWI and the ADC can help in the differential diagnosis of particular disorders (such as carcinomas vs lymphomas, or necrosis vs abscess) of the head and neck. The ADC can also provide further information to help differentiate benign from malignant tumors, as ADC values are usually lower in cases of malignancy. However, the ADC is itself influenced by various complex factors such as the cellularity and matrix of tumors and there is also some overlap between certain benign and malignant tumors of the salivary glands.