Introduction. Cancer rehabilitation programs mainly involve endurance training, and little attention is paid to strength training. Cancer survivors are generally advised to train at much lower workloads than the standard guidelines for strength training suggest. The purpose of this study is to evaluate the effectiveness of an 18-week high-intensity strength training program in cancer survivors. Methods. Fifty-seven patients (age 24 to 73 years) who had received chemotherapy for lymphomas, breast, gynecologic, testicular, or colorectal cancer completed the program. Outcome measures were changes in muscular strength (one-repetition maximum), cardiopulmonary function (VO(2) max), maximal short exercise capacity (MSEC), body composition and health-related quality of life (HRQOL) between baseline and follow-up. Discussion. The high-intensity strength training was well tolerated by all patients. Significant improvements in muscle strength were found, with effect sizes varying from 1.32 to 2.68. VO(2) max increased significantly by 10% in men and by 13% in women. Different functional scales of HRQOL improved (p < 0.01), with effect sizes varying from 0.47 to 0.82. Muscle strength correlated significantly with physical functioning before and after the training program. Conclusion. We conclude that a supervised, high-intensity strength training program seems to be an effective means to improve muscle strength, cardiopulmonary function, and HRQOL and should be incorporated in cancer rehabilitation programs. Further randomized trials are needed to confirm the results.