Background: There is great overlap between the presentation of cachexia, sarcopenia, and malnutrition. Distinguishing between these conditions would allow for better targeted treatment for patients. Objectives: The aim was to systematically review validated screening tools for cachexia, sarcopenia, and malnutrition in adults and, if a combined tool is absent, make suggestions for the generation of a novel screening tool. Design: A systematic search was performed in Ovid Medline, EMBASE, CINAHL, and Web of Science. Two reviewers performed data extraction independently. Each tool was judged for validity against a reference method. Psychometric evaluation was performed as was appraisal of the tools' ability to assess the patient against consensus definitions. Results: Thirty-eight studies described 22 validated screening tools. The Cachexia score (CASCO) was the only validated screening tool for cachexia and performed well against the consensus definition. Two tools assessed sarcopenia [the Short Portable Sarcopenia Measure (SPSM) and the SARC-F (Strength, Assistance with walking, Rise from a chair, Climb stairs, and Falls)] and scored well against the 1998 Baumgartner definition. The SPSM required large amounts of equipment, and the SARC-F had a low sensitivity. Nineteen tools screened for malnutrition. The 3-Minute Nutrition Score performed best, meeting consensus definition criteria (European Society for Clinical Nutrition and Metabolism) and having a sensitivity and specificity of >80%. No tool contained all of the currently accepted components to screen for all 3 conditions. Only 3 tools were validated against cross-sectional imaging, a clinical tool that is gaining wider interest in body-composition analysis. Conclusions: No single validated screening tool can be implemented for the simultaneous assessment of cachexia, sarcopenia, and malnutrition. The development of a tool that encompasses consensus definition criteria and directs clinicians toward the underlying diagnosis would be optimal to target treatment and improve outcomes. We propose that tool should incorporate a stepwise assessment of nutritional status, oral intake, disease status, age, muscle mass and function, and metabolic derangement.