Background: Arteriovenous fistulas (AVFs) are important vascular access routes for patients undergoing maintenance haemodialysis. However, complications such as thrombosis, stenosis, infection and pseudoaneurysm may compromise fistula function. Doppler ultrasonography provides non-invasive anatomical and haemodynamic assessment of vascular access. Aim: To evaluate arteriovenous haemodialysis fistulas using Doppler ultrasonography, determine the prevalence and pattern of complications, and assess associations between Doppler parameters, clinical characteristics and fistula complications. Materials and Methods: This cross-sectional observational study was conducted at a tertiary care hospital from May 2024 to October 2025. Seventy adult patients with end-stage renal disease undergoing haemodialysis through an AVF were included. Doppler assessment evaluated blood flow, peak systolic velocity at the anastomosis, brachial artery resistive index, draining vein diameter and skin-to-fistula vein distance. Demographic and clinical variables were also recorded. Statistical analysis was performed using R software, with appropriate tests for continuous and categorical variables. Results: The mean age was 55 ± 13 years, and 64.3% of participants were male. Radiocephalic fistulas were the most common type (51.4%). Complications were identified in 14 patients (20%). Thrombosis was the most frequent complication (35.7%), followed by stenosis and perifistula haematoma (21.4% each). Mean fistula blood flow was significantly lower in patients with complications than in those without complications (688 ± 298 versus 831 ± 273 mL/min; p = 0.049). Diabetes mellitus was also associated with complications (p = 0.028). Other evaluated Doppler parameters did not demonstrate statistically significant differences between groups. Conclusion: Doppler ultrasonography identified fistula complications and provided useful haemodynamic information. Lower blood flow and diabetes mellitus were associate