Interleukin-18 (IL-18) is an immune-stimulatory cytokine with antitumor activity in preclinical models. It plays pivotal roles in linking inflammatory immune responses and tumor progression and is a useful candidate in gene therapy of lymphoma or lymphoid leukemia. A phase I study of recombinant human IL-18 (rhIL-18) in patients with advanced cancer concluded that rhIL-18 can be safely given in biologically active doses to patients with advanced cancer. Some viruses can induce the secretion of IL-18 for immune evasion. The individual cytokine activity might be potentiated or inhibited by combinations of cytokines. Here we focus on combinational effects of cytokines with IL-18 in cancer progression. IL-18 is an important non-invasive marker suspected of contributing to metastasis. Serum IL-18 may a useful biological marker as independent prognostic factor of survival. In this review we cover roles of IL-18 in immune evasion, metastasis and angiogenesis, applications for chemotherapy and prognostic or diagnostic significance.