Substantial uncertainty exists about prevalence of mood disorders in patients with cancer, including those in oncological, haematological, and palliative-care settings. We aimed to quantitatively summarise the prevalence of depression, anxiety, and adjustments disorders in these settings. We searched Medline, PsycINFO, Embase, and Web of Knowledge for studies that examined well-defined depression, anxiety, and adjustment disorder in adults with cancer in oncological, haematological, and palliative-care settings. We restricted studies to those using psychiatric interviews. Studies were reviewed in accordance with PRISMA guidelines and a proportion meta-analysis was done. We identified 24 studies with 4007 individuals across seven countries in palliative-care settings. Meta-analytical pooled prevalence of depression defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM) or International Classification of Diseases (ICD) criteria was 16·5% (95% CI 13·1-20·3), 14·3% (11·1-17·9) for DSM-defined major depression, and 9·6% (3·6-18·1) for DSM-defined minor depression. Prevalence of adjustment disorder alone was 15·4% (10·1-21·6) and of anxiety disorders 9·8% (6·8-13·2). Prevalence of all types of depression combined was of 24·6% (17·5-32·4), depression or adjustment disorder 24·7% (20·8-28·8), and all types of mood disorder 29·0% (10·1-52·9). We identified 70 studies with 10,071 individuals across 14 countries in oncological and haematological settings. Prevalence of depression by DSM or ICD criteria was 16·3% (13·4-19·5); for DSM-defined major depression it was 14·9% (12·2-17·7) and for DSM-defined minor depression 19·2% (9·1-31·9). Prevalence of adjustment disorder was 19·4% (14·5-24·8), anxiety 10·3% (5·1-17·0), and dysthymia 2·7% (1·7-4·0). Combination diagnoses were common; all types of depression occurred in 20·7% (12·9-29·8) of patients, depression or adjustment disorder in 31·6% (25·0-38·7), and any mood disorder in 38·2% (28·4-48·6). There were few consistent correlates of depression: there was no effect of age, sex, or clinical setting and inadequate data to examine cancer type and illness duration. Interview-defined depression and anxiety is less common in patients with cancer than previously thought, although some combination of mood disorders occurs in 30-40% of patients in hospital settings without a significant difference between palliative-care and non-palliative-care settings. Clinicians should remain vigilant for mood complications, not just depression. None. Copyright © 2011 Elsevier Ltd. All rights reserved.