Dendritic cells play a central role in the presentation of antigen to naïve T-cells and the induction of primary immune responses. Preclinical studies have established that dendritic cells loaded with antigens ex vivo induce potent antitumor and antiviral immune responses in vitro and in vivo. This has lead to a proliferation of clinical trials testing their effectiveness in humans, particularly with advanced malignancies. The few reported studies suggest that clinically relevant immune responses may be induced against some types of malignancies. Many questions regarding the best type of dendritic cell, degree of maturity, choice of antigen, route and schedule of administration, targeting to lymphoid tissue and use of additional adjuvants will need to be answered in preclinical and clinical studies as the field of dendritic cell-based immunotherapy progresses.