Patients subjected to allogeneic hematopoietic stem cell transplantation (HSCT) are at increased nutritional risk which in turn may alter their outcome. For providing good nutritional care for patients, it is important to analyze risk factors influencing nutritional status during and after HSCT. Fifty patients undergoing allogeneic HSCT were subjected to nutritional status assessment by using the patient-generated subjective global assessment (PG-SGA) at initial admission, day 30 and day 180. Two patients (4%) had malnutrition at admission, 36 (72%) at day 30, and 24 (48%) at day 180. At day 30, comorbidity index higher than 0 and fever lasting for more than 1 week had a significant impact on nutritional status (P = .004 and P = .006, respectively). Regarding day 180, comorbidity index higher than 0 and presence of >= grade II acute gastrointestinal graft versus host disease (GI GVHD) significantly influenced nutritional status (P = .017 and P = .026, respectively). Well-nourished patients at admission and day 180 had a significantly higher overall survival (OS) in comparison to malnourished patients (P < .001 and P = .012, respectively). Nutritional status at admission and day 180 had a significant influence on OS in multivariate analysis (P = .039 and P = .032, respectively). Allogeneic HSCT patients having high comorbidity index, developing prolonged fever, and experiencing >= grade II acute GI GVHD suffer from worsening in their nutritional status during hospitalization and after discharge. Also, nutritional status at admission and day 180 significantly influences their survival.