Prognostication is an important clinical skill for all clinicians, particularly those clinicians working with patients with advanced cancer. However, doctors can be hesitant about prognosticating without a fundamental understanding of how to formulate a prognosis more accurately and how to communicate the information with honesty and compassion. Irrespective of the underlying type of malignancy, most patients with advanced cancer experience a prolonged period of gradual decline (months/years) before a short phase of accelerated decline in the last month or two. The main indicators of this final phase are poor performance status, weight loss, symptoms such as anorexia, breathlessness or confusion and abnormalities on laboratory parameters (e.g. high white cell count, lymphopaenia, hyopalbuminaemia, elevated lactate dehydrogenase or C-reactive protein). The clinical estimate of survival remains a powerful independent prognostic indicator, often enhanced by experience, but research has only begun to understand the different biases affecting clinicians' estimates. More recent research has shown probabilistic predictions to be more accurate than temporal predictions. Simple, reliable and valid prognostic tools have been developed in recent years that can be used readily at the bedside of terminally ill cancer patients. The greatest accuracy occurs with the use of a combination of subjective prognostic judgements and objective validated tools. Communicating survival predictions is an important part of cancer care and guidelines exist for improving delivery of such information. Important cultural differences may influence communication strategies and should be recognised in clinical encounters. More well-designed studies of prognosis and its impact on decision making are needed. The benefits and limitations of prognostication should be considered in many clinical decisions.