Cancer of unknown primary sites (CUP) is a compilation of various malignant entities--the majority of which behave aggressively and carry poor prognosis. CUP is classified into two different clinicopathological groups: the unfavourable (poor-prognosis) and the favourable (good-prognosis) group. Patients with favourable subsets are treated relevant to the hidden primary tumour chemotherapy regimens and/or radiotherapy. These patients exhibit better responses and prolonged survival. On the other hand, patients of unfavourable subsets are treated with various chemotherapy combinations of platinum- or taxane-containing regimens. Unfortunately, responses and overall survival in this group of CUP patient are not very promising. Several independent prognostic factors have been associated with survival of CUP patients. Since CUP is not an unknown disease, emerging therapeutic innovations are warranted.