Introduction. The study checked whether there is a relationship between an easily accessible parameter like Body mass index BMI and the diameter of the femoral head. Material and methods. the data of 47 consecutively surgically treated patients from the Department of Orthopedics, Traumatology and Oncology of the Motor Mechanism of the Pomeranian Medical University who underwent total hip arthroplasty were analyzed. Patients were divided into two groups: group I-26 women and group II-21 men. The diameter of the femoral head was measured intraoperatively with a caliper. Body weight and height were measured the day before the planned surgery. Results. Average age-65.77 (± 13.84) years in women, 65.95 (± 11.61) years in men. Mean BMI-27.57 (± 4.14) in women, 28.86 (± 4.80) in men. In group I (21 men) there was no statistically significant correlation between BMI and femoral head diameter (p = 0.305). However, there was a strong positive correlation (r = 0.6279, p = 0.02) between the height and diameter of the femoral head. In Group II (26 women), a moderately positive correlation (r = 0.4301, p = 0.028) was found between BMI and the diameter of the femoral head. In addition, there was a strong positive correlation between the diameter of the femoral head and height (r = 0.6873, p = 0.0001) and body weight, and the diameter of the femoral head (r = 0.5904, p = 0.01). Conclusions. Men in comparison to women, despite similar mean BMI and age, had statistically significant (p = 0.000003) higher mean size of femoral head-diameter of femoral head in women = 47.65 (± 3.91) and men, 53.19 (± 2.74). Increased BMI suggests that the diameter of the femoral head is also larger, but only in women. However, a more universal parameter is growth because it showed a strong positive correlation with the value of the diameter of the femoral head in both the group of women and men.