This study compares the clinical functionality of three commercially available treatment-planning systems: Phillip's Pinnacle ³ (trademark), Best NOMOS CORVUS, and Varian Eclipse for intensity modulated radiation therapy (IMRT) treatment planning. The study considers machine commissioning, dose optimization, dose calculation and plan assessment. All three treatment planning systems were commissioned using Varian's Golden Beam data for the same 6 MV photon beam produced by the Varian Medical Systems' Trilogy linear accelerator, which is equipped with a high resolution multileaf collimator. Three patients' test plans, each with specified imaging, contour information, and optimization parameters were used. The resulting isodose distributions and dose volume histograms were compared to evaluate the optimization algorithms. Film dosimetry was used to verify the accuracy of planned to actual dose distributions. Efficiency was analyzed by comparing the resulting monitor units for each plan to a benchmark conventional plan. This study provides a concise analysis of IMRT planning for the three different treatment planning systems and can assist users in choosing which is best for their institution.