Aim: Our objective was to determine the factors associated with the successful maturation of arteriovenous fistulas during hemodialysis. Material and methods: This prospective study included patients treated with hemodialysis and predialysis patients. Clinical, biochemical, sociodemographic, vascular ultrasound mapping, flow-mediated dilatation, and surgical factors were analyzed. Success in the maturation process was defined by ultrasonographic criteria at six weeks. Results: Thirty-seven patients were included. With a mean ± standard deviation age of 40 ± 14 years, 73% were male, 65% had type-2 diabetes mellitus, and 95% had hypertension. Arteriovenous fistulas were brachycephalic in 18 patients (49%), brachymedian in nine patients (24%), brachycommunicating posterior in five patients (14%), brachibasal in three patients (8%), radiocephalic in two patients (8%), and radiocephalic in two patients (5%). Fourteen percent of patients had unsuccessful maturation. The vein diameter was 4.3 ± 1.0 mm (maturation group) vs 3.2 ± 0.9 mm (non-maturation group), p = 0.04. The artery diameter was similar: 4.5 ± 0.6 vs 4.5 ± 0.4, p = 0.88. Logistic regression analysis revealed that the diameter of the vein for which the surgery was performed was the factor associated with successful maturation in our population, odds ratio = 4.77 (1.14–19.97), p-value = 0.032. Conclusions: It is highly important to plan vascular access in patients to perform vascular mapping and measure veins and arteries in patients. Vein measurement is a significant factor in successful maturation of the arteriovenous fistulas.