Background/Aims: The effects of haemodialysis on the microcirculation are poorly understood. This study examined the changes in small vessel calibre. Methods: 24 patients (including 12 males, median age 62.5 years, range 30–87) underwent digital retinal photography immediately before and after routine haemodialysis. Arteriolar and venular calibres were measured from the images by a trained grader using a highly reproducible, computer-assisted method. Results: Patients had an average 2.0 ± 0.3 litres of fluid removed with dialysis, and their mean arterial blood pressure fell by 6.8 mm Hg (CI 13.8–0.2, p = 0.06). Retinal arteriole calibre did not change (mean difference 2.3 µm, CI –1.1 to 5.7, p = 0.17) but the venules dilated (mean difference 12.7 µm, CI 7.3–18.3, p < 0.001). Calibre returned to baseline by 2 h. Venules dilated less in diabetics than non-diabetics (mean difference –6.2 µm, CI –9.6 to –2.9, p < 0.01). Retinal venular dilatation correlated positively with the volume of fluid removed per kilogramme body weight (5.9, CI 0.2–11.5, p = 0.04), and negatively with the fall in mean arterial pressure (–0.36, CI –0.72 to –0.01, p < 0.05) after adjusting for age, gender, diabetes and dyslipidaemia. Conclusion: Haemodialysis is associated with systemic venular dilatation.