PURPOSE: The treatment of moving targets with intensity-modulated radiotherapy may introduce errors in dose delivery. The motion of tumors in the abdomen was studied using quantitative fluoroscopic analysis, and the effect on dose delivery to the target was studied. METHODS AND MATERIALS: Fluoroscopy sessions for 7 patients with pancreas or liver tumors and fiducial clips were recorded, converted to digital format, and analyzed to quantify the characteristics of tumor motion. Intensity-modulated radiotherapy plans were generated for 3 patients (a total of five plans), and the dose-volume histograms for the target volume were compared between plans with and without tumor motion. RESULTS: The average magnitude of the peak-to-peak motion for the 7 patients in the craniocaudal and AP directions was 7.4 mm and 3.8 mm, respectively. The clip motion varied widely, because the maximal clip excursions were about 47% greater than the average clip excursions for each patient. The inclusion of tumor motion did not lead to a significant degradation in the target dose-volume histogram for four of five treatment plans studied. CONCLUSION: The amount of tumor motion for most patients in this study was not large but could, in some instances, significantly degrade the planned target dose-volume histogram. For some patients, therefore, motion mitigation or intervention during treatment may be necessary.