Methods: We systematically reviewed studies assessing the prevalence of mental health conditions in acute care hospitals with comprehensive structured clinical interviews. Results: Of 46 retrieved manuscripts, eight were deemed eligible for this meta-analysis. Within the studies, 1448 cancer patients had been assessed, whereby 456 were diagnosed having a mental health disorder. The prevalence rates ranged from 23% (breast cancer patients in Turkey) to 53% (elderly cancer patients in Uganda). The combined prevalence estimate is 32% (95% confidence interval 27% to 37%). Conclusion: One-third of the cancer patients in acute care hospitals is suffering from mental health disorders and need appropriate treatment.