The aim of this study was to investigate the movement, and the factors that influence such movement, of pancreatic lesions and to provide a reference for determination of planning target volume (PTV) during stereotactic radiotherapy. We implanted 19 gold markers into the inner pancreatic tumours of 16 pancreatic carcinoma patients percutaneously under B-ultrasonographic guidance. The marked motion of pancreatic lesions in the x (right-left), y (superoinferior) and z (anteroposterior) directions was measured using an X-ray simulator system. Based on the statistical analysis of the detected movements, we investigated the relevant influencing factors of pancreatic lesions with multinomial linear regression. Data showed that the mean motion amplitudes of pancreatic lesions were 0.16 cm +/- 0.06 (range 0.1-0.3 cm) in the x direction, 0.25 cm +/- 0.12 (range 0.1-0.4 cm) in the y direction and 0.88 cm +/- 0.24 (0.5-1.6 cm) in the z direction. Motion amplitude was not correlated with the height, weight or age of the patients nor with the location or size of the tumour. The motion of pancreatic lesions was mainly influenced by the respiratory motion and has maximal amplitude in the z direction. Therefore, motion in the z direction should be given a priority consideration while determining the PTV.