Oncolytic viruses possess an inherent trophism for tumor cells or have been engineered in a variety of ways to selectively replicate in and destroy cancer cells. Because of the unique mode of tumor destruction, oncolytic virotherapy has the potential to augment the antineoplastic activity of chemotherapy and radiation therapy. Many oncolytic viruses, such as adenovirus, HSV, vaccinia, measles, reovirus, Newcastle disease virus and coxsackie virus, have entered into clinical trials and their efficacy and safety have been demonstrated with few, minor, side effects. Data obtained from several clinical trials of the oncolytic adenovirus, ONYX-015, in patients with cancer have been described in detail. Some preclinical studies of oncolytic viruses have demonstrated promising results, mainly when administered in combination with chemotherapeutic drugs. In this review, the clinical use of oncolytic viruses in combination with chemotherapy and radiation therapy, and future directions to enhance the efficacy of oncolytic virotherapy, are discussed.