This study aimed to investigate and compare the sonographic appearances of parotid glands in nasopharyngeal carcinoma patients treated with conventional radiotherapy (RT) or intensity-modulated radiotherapy (IMRT), and to compare them with healthy subjects. Totally 43 patients treated with conventional RT, 38 patients treated with IMRT and 58 healthy subjects were recruited and underwent parotid ultrasonography. Parotid glands were assessed for their size, echogenicity and internal architectures. The mean transverse dimension of parotid glands in patients treated with conventional RT and those treated with IMRT were significantly smaller than that in healthy subjects (p