The goal of this study was to evaluate the use of multi-criteria optimization (MCO) in the planning and optimization of intensity-modulated radiotherapy (IMRT). Twenty (20) IMRT patients (ten (10) with prostate cancer and ten (10) with lung cancer) were randomly selected. The treatment plans for these patients were designed using direct machine parameter optimization (DMPO). Based on these plans, new plans were designed using multi-criteria optimization (MCO), keeping the optimization objectives and constraints unchanged. Comparisons were made between the new plans, which were based on MCO and DMPO, including the dose distribution, dose volume histogram (DVH), the optimization time and the number of monitor units (MUs). The plan designed using both optimization approaches satisfied all clinical requirements. For similar or better target coverage, the rectum, bladder and small bowel were better protected using MCO than when using DMPO. Additionally, MCO reduced the time for optimization by 58% on average, whereas the MUs increased the time for optimization by 32% on average for prostate cancer. For lung cancer cases, the entire lung, heart and spinal cord were better protected using MCO compared to DMPO. Similarly, MCO reduced the time for optimization by 59% on average, whereas the MUs increased the time for optimization by 11% on average. Compared to DMPO, MCO reduces the dose of the organs at risk (OAR) and shortens the time required for optimization.