The prevalence of obesity is increasing worldwide and it is known to be associated with many postoperative complications, including infection. Patients' body fat distribution may vary and body mass index (BMI) does not provide sufficient information about adipose tissue thickness of the lower extremities. The aim of this study is to investigate the relationship between thigh diameters and early postoperative prosthesis-related joint infections (PJI) in patients who underwent arthroplasty. The study included 76 patients and 114 knees who were operated on by a single surgeon and underwent total knee arthroplasty (TKA) due to primary knee osteoarthritis between May 2022 and September 2023 in a tertiary reference hospital. Circumference of the thickest part of the operated thigh (cm), preoperative erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, height, weight, BMI and the presence of early postoperative prosthesis-related joint infections were evaluated. The mean BMI was 32.6 ± 4.2 (kg/m2). Two (2.6%) were normal weight, 14 (18.5%) were overweight, 58 (76.3%) were obese and 2 (2.6%) were morbidly obese. The mean circumference of the thickest part of the thigh was 57.56 ± 6.38 (cm). 6 patients were diagnosed with PJI in the acute phase. The mean circumference of the thickest part of the thigh was statistically significantly greater in the group with acute PJI compared to the group without PJI (p = 0.048). The incidence of acute PJI was found to be significantly higher in patients with larger thigh diameters, whereas no such relationship was observed for BMI. The incorporation of preoperative soft tissue envelope measurements into routine clinical examination may prove beneficial in reducing the risk of PJI.