We aimed to assess the clinical usefulness of the ADCs calculated from diffusion-weighted echo-planar MR images in the characterization of pediatric head and neck masses. This study included 78 pediatric patients (46 boys and 32 girls aged 3 months-15 years, mean 6 years) with head and neck mass. Routine MR imaging and diffusion-weighted MR imaging were done on a 1.5-T MR unit using a single-shot echo-planar imaging (EPI) with a b factor of 0.500 and 1,000 s mm(-2). The ADC value was calculated. The mean ADC values of the malignant tumours, benign solid masses and cystic lesions were (0.93 +/- 0.18) x 10(-3), (1.57 +/- 0.26) x 10(-3) and (2.01 +/- 0.21 ) x 10(-3) mm(2) s(-1), respectively. The difference in ADC value between the malignant tumours and benign lesions was statistically significant (p < 0.001). When an apparent diffusion coefficient value of 1.25 x 10(-3) mm(2) s(-1) was used as a threshold value for differentiating malignant from benign head and neck mass, the best results were obtained with an accuracy of 92.8%, sensitivity of 94.4%, specificity of 91.2%, positive predictive value of 91% and negative predictive value of 94.2%. Diffusion-weighted MR imaging is a new promising imaging approach that can be used for characterization of pediatric head and neck mass.