BACKGROUND: Hematopoietic stem cell transplantation frequently necessitates nutritional support. However, the safety and tolerance of parenteral nutrition have not been adequately examined, except for its association with infectious complications. AIM: To evaluate the impact of parenteral nutrition on nutritional status and its correlation with complications during the early period following hematopoietic stem cell transplantation. MATERIALS AND METHODS: From 2019–2020, 125 recipients of autologous (n=38) and allogeneic (n=87) hematopoietic stem cell transplantation were included in the study with a median age of 20 years (2–65). The chosen cohort included patients with leukemia (n=67), solid tumors (n=32), dysplasia (n=15) and lymphoproliferation (n=11). The control group (n=55) was composed of patients who did not depend on nutritional support. Parenteral nutrition was administered to the primary group (n=70) using second-generation (n=22) and third-generation (n=24) fat emulsions. In the event of contraindications, parenteral nutrition was administered without fat emulsions (n=24). To mitigate the risk of side effects, the initial dose of parenteral nutrition was 50%, with the achievement of the complete dose by the third day of therapy. RESULTS: In 95.7% of cases, mucositis was the indication for parenteral nutrition. The duration of parenteral nutrition was 2–31 days (median, 11 days). In 58.6% of cases, parenteral nutrition was initiated against the background of nausea and vomiting. During the escalation of the parenteral nutrition dose, increased nausea was observed in 7.1% of patients. Side effects were noted in 22.9% of cases: hyperglycemia (n=7), vomiting (n=6) and hypertriglyceridemia (n=3). Four patients developed complications associated with parenteral nutrition, and nutritional therapy was discontinued in 20% of cases (n=14). After hematopoietic stem cell transplantation, the primary clinical efficacy criterion, body mass index, was observed to decline in each observation group. However, it recovered by day 28 and did not differ between the comparison groups as follows: the control group — from 22.7±6.4 to 21.7±6.1 kg/m2, (p=0.42); group “2 in 1” — from 23.4±6.1 to 21.6±4 kg/m2, (p=0.56); group provided with parenteral nutrition employing second-generation fat emulsions — from 18,8±4,9 to 18.7±4.4 kg/m2, (p=0.72); group administered parenteral nutrition with third-generation fat emulsions — from 18.6±4.2 to 18.3±3.5 kg/m2, (p=0.84). The febrile neutropenia rate was 75.2% and did not vary in the control and comparison groups (p=0.54). The incidence of sepsis was 24.8% and was not influenced by the use of parenteral nutrition (p=0.07). Furthermore, sepsis risk was higher when administering parenteral nutrition “2 in 1” compared to fat emulsions-containing parenteral nutrition (p=0.002). The overall frequency of acute graft versus host disease was 16.1% and was similar in the comparison groups (p=0.65). CONCLUSION: In the cohort of patients treated with hematopoietic stem cell transplantation, parenteral nutrition regimens supplemented with second- and third-generation fat emulsions with a stepwise dose increase varied in acceptable tolerance, infection-related complications, and immunological safety, as well as effectively maintained nutritional status parameters.