Background/Aim: Aneurysms are known manifestations of autosomal dominant polycystic kidney disease (ADPKD). We investigated whether the dimensions of arteriovenous fistulas created for performance of haemodialysis were affected by the original disease. Methods: The lumen diameter of the fistula was studied by ultrasound in 19 patients with ADPKD and in 19 control patients. The patients’ sex, age, the duration of their fistulas, haemoglobin values and blood pressure levels were similar in both groups. The monitoring was performed along the forearm part of the vein, and the maximal diameter was measured. The diameters at the two needle insertion sites were also measured. Results: The ADPKD patients had a significantly higher fistula diameter than the control patients: 12 (range 8–19) mm versus 8 (range 6–24) mm at the widest level (p = 0.003). There were no significant differences in the diameters at the needle insertion sites. Conclusion: The receiving veins of arteriovenous fistulas in patients with ADPKD have an abnormality that causes a greater than normal dilatation in response to the arterialization. We postulate that this phenomenon is linked with the increased prevalence of aneurysms in ADPKD.