Sarcopenia, low muscle mass, and low muscle radiodensity are increasingly being considered factors associated with treatment outcomes in patients with gynecological malignancies. Despite the growing body of evidence, body composition assessment is not routinely incorporated into clinical practice. The aim of this review was to present current evidence on the associations of muscle parameters with survival, complications, systemic treatment toxicity, and quality of life, as well as to discuss the opportunities and limitations of computed tomography (CT) and bioelectrical impedance analysis (BIA) in body composition monitoring. A narrative literature review was conducted using the PubMed, Scopus, and Web of Science databases, primarily covering publications from 2019 to 2026, together with earlier studies relevant to the topic. Systematic reviews, meta-analyses, and selected observational, longitudinal, and interventional studies were included. The available evidence indicates that low muscle mass and low muscle radiodensity are primarily associated with poorer overall survival and an increased risk of selected postoperative complications. Evidence regarding progression-free survival, disease recurrence, chemotherapy toxicity, and quality of life remains less consistent. Low muscle mass may occur independently of body weight and body mass index (BMI); therefore, routine anthropometric assessment may fail to identify adverse changes in body composition. CT image analysis enables quantitative assessment of muscle mass and evaluation of muscle radiodensity, whereas BIA may serve as a complementary tool for repeated body composition monitoring. However, its use is limited by the effects of hydration status, edema, and ascites, as well as by the lack of validated cut-off values for patients with gynecological malignancies. Body composition assessment should be interpreted in conjunction with evaluations of muscle strength, physical performance, nutritional status, treatment toxicity, and quality of life. Prospective studies are needed to determine whether body composition monitoring and the implementation of targeted supportive care improve treatment tolerance and clinical outcomes.