Many health professionals (HPs) express discomfort at having to broach the topic of prognosis, including limited life expectancy, and may withhold information or not disclose prognosis. A systematic review was conducted of 46 studies relating to truth-telling in discussing prognosis with patients with progressive, advanced life-limiting illnesses and their caregivers. Relevant studies meeting the inclusion criteria were identified by searching computerized databases (MEDLINE, EMBASE, CINAHL, PsychINFO and Cochrane Register of Controlled Trials) up to November 2004, with handsearching of studies, as well as inclusion of studies satisfying selection criteria reported in 2005 by the authors. The reference lists of identified studies were hand-searched for further relevant studies. Inclusion criteria were studies of any design evaluating communication of prognostic information that included adult patients with an advanced, life-limiting illness; their caregivers; and qualified HPs. Results showed that although the majority of HPs believed that patients and caregivers should be told the truth about the prognosis, in practice, many either avoid discussing the topic or withhold information. Reasons include perceived lack of training, stress, no time to attend to the patient's emotional needs, fear of a negative impact on the patient, uncertainty about prognostication, requests from family members to withhold information and a feeling of inadequacy or hopelessness regarding the unavailability of further curative treatment. Studies suggest that patients can discuss the topic without it having a negative impact on them. Differences and similarities in findings from different cultures are explored.