Introduction. In patients who have undergone hematopoietic cell transplantation (HCT), the metabolic syndrome may develop without obesity defined by Body Mass Index (BMI). Aim of the study. The aim of the study was to compare body fat parameters measured using bioelectrical impedance (BIA) and using standard parameters of obesity in patients treated with HCT and healthy controls. Material and methods. We compared body fat (BF) and body fat percentage (BF%) measured using BIA in 44 patients before HCT and 28 patients after HCT, versus 26 controls. We also compared BMI and other BIA parameters in these groups of patients. Results. The differences in BF and BF% between the patients before HCT and controls were not significant, while both BF and BF% were significantly lower in patients after HCT than in the control group. No significant differences in standard clinical obesity parameters were found in the patients before HCT, and in the patients after HCT, compared with the controls. The differences in other BIA parameters between the patients before HCT and the controls were not significant, while in the patients after HCT some parameters were significantly lower. Conclusion. Significant differences in BF and BF% in the patients after HCT compared with healthy controls suggest that BIA may be useful in screening for body fat abnormalities in patients after HCT.