Cancer patients are highly vulnerable to weight loss and malnutrition, before chemotherapy, thus reducing overall survival (OS). The objective was assessing weight loss and OS prognostication in gastric cancer patients at baseline of chemotherapy treatment. Observational retrospective study with patients who were treating in cancer public clinic in Brazil, was evaluated weight loss and cachexia. It was evaluated by sex, BMI, grade system classification (GSC) and stage the OS by Kaplan-Meier method and Cox proportional hazards model. Ninety-two patients, 73.9% were male. At baseline chemotherapy patients have presented 15.3% of body weight loss, 28.3% were malnourished, 86.8% classified witch cachexia, 80.3% were grade 3-4 in GSC and 86.9% at cancer stage 3-4. OS was lower for male (15.9 mo.), malnourished (12.0 mo.), GCS-4 (16.3 mo.) and Stage 4 (13.3 mo.) patients. GSC grade four and BMI classification to underweight comparing obesity are associated with reduced OS, together to male sex and cancer stage 4, have gotten together shown that seems to confer a survival disadvantage to other patients in these parameters too. Cox regression analysis have not shown statistical significance for sex, Initial BMI Class, GSC, cancer stage. Gastric cancer patients at chemotherapy treatment outset present high weight loss, cachexia prevalence and OS reduction.