¡¾Abstract¡¿ AIM: To measure the setup error in the intensity modulated radiation therapy (IMRT) for headª²neck neoplasms, and to analyze the margin between the clinical target volume (CTV) and planning target volume (PTV). METHODS: Seventyª²six patients with headª²neck neoplasms were choosed at random. The portal films were screened using the electronic portal imaging device (EPID), and the error was analyzed through comparing the portal film with the digitally reconstruced radiographs (DRR) in the treatment planning system (TPS). RESULTS: The setup errors were (-0.62¡À1.46) mm,(-0.41¡À1.54) mm,(-0.31¡À1.67) mm and the margins were 2.27 mm, 1.87 mm, 1.98 mm in lateral, cranialª²caudal and ventralª²dorsal directions respectively. CONCLUSION: For the patients with headª²neck neoplasms undergoing the IMRT, the margins between the CTV and the PTV should be 2.5 mm in the lateral direction, and 2 mm in cranialª²caudal and ventralª²dorsal directions. Moreover, with the treatment time goes by, the error varied irregularly. ......