BACKGROUND: Sarcopenia, defined as loss of skeletal muscle mass and associated with lower outcomes in gastrointestinal tumors. This study aimed to show the effects of sarcopenia on prognosis, morbidity, and mortality in patients diagnosed with gastric cancer in light of these data. METHODS: This single-center retrospective cohort study evaluated patients aged 18 to 80 years who were diagnosed with gastric cancer between 2010 and 2015. Preoperative CT images of the patients were examined. The muscle area was calculated at the L3 vertebra level on CT images the values of <43 cm2/m2 for men and <41 cm2/m2 for women, which were determined and shown to be associated with reduced survival, on the tomography scans obtained from all oncological patients for screening purposes. RESULTS: The SMI ranged from 26.2 to 73.8 (cm2/m2) in men and 24.8 to 55.07 (cm2/m2) in women. The mean SMI was 48.97 (cm2/m2) in men and 39.07 (cm2/m2) in women. Among study patients, 43 men and 33 women were sarcopenic. Sarcopenia was statistically significantly more common in men than in women. Comorbidities were more common in the Sarcopenic group. However, there was no statistically significant difference (p = 0.49). In the Sarcopenic group, forty-nine patients were referred to neoadjuvant therapy, while fifty-three patients were referred to neoadjuvant therapy in non-sarcopenic group. CONCLUSION: The present study shows the effects of CT-based measured sarcopenia on short- and long-term outcomes in gastric cancer patients. It is believed that the detection and correction of sarcopenia in these patients would positively affect the early and late outcomes.