Background: The evidence that body composition parameters influence multiple cancer outcomes is rapidly expanding. Excess adiposity deposits in muscle tissue, termed myosteatosis, can be detected in CT scans through variations in the density of muscle tissues (Hounsfield Units). Patients with similar muscle mass but different amounts of intramuscular adipose infiltration have increased chemotherapy toxicity, time to tumor progression and other adverse outcomes among different cancer types. Our review examines the impact of myosteatosis on overall survival (OS) in patients with cancer. Methods: A systematic search of the literature was conducted on PubMed/ MEDLINE, Cochrane CENTRAL, and EMBASE. Meta-analysis was conducted using a random-effects model. Risk of bias was evaluated using the Newcastle-Ottawa Quality assessment for cohort studies, funnel plot (publication bias), and GRADE summary of findings tool from Cochrane. Results: A total of 4880 articles were screened from which 40 articles selected, including 21,222 patients. The overall mean proportion of patients with myosteatosis was 48 % (range 11–85 %). Using skeletal muscle density (SMD), patients classified as having myosteatosis had 75 % greater mortality risk compared to non-myosteatosis patients (HR 1.75 95 % CI 1.60–1.92, 40 studies) (p < .00001) (i2 = 62 %). Specifically, myosteatosis was prognostic for worse OS in patients with gynecological, renal, periampullary/pancreatic, hepatocellular, gastroesophageal, and colorectal carcinoma, and lymphomas. Conclusion: Our analysis of the literature shows that cancer patients with myosteatosis have shorter survival. Our findings suggest that in oncological practice, muscle density assessment is valuable as a prognostic parameter.