['Acquired cystic kidney disease (ACKD) is a frequent complication in chronic hemodialysis (HD) patients and a risk factor for renal cell carcinoma. Online hemodiafiltration (HDF) provides better clearance of middle molecular weight solutes, but its effect on ACKD has not been investigated.', 'This case-control study enrolled 86 patients (43 HDF patients and 43 HD patients) who were matched according to age, sex, and duration of renal replacement therapy. The mean duration of HDF was 63 (+/- 35) months. The frequency and severity of ACKD was evaluated by ultrasonography using a severity scoring system.', 'We observed ACKD in 23 of the HD patients (53.5%) and 21 of the HDF patients (48.8%). This difference was not statistically significant (p = 0.829). The overall ACKD severity scores were similar in the two groups (p = 0.875). Patients on HDF had significantly lower serum levels of alkaline phosphatase and intact parathyroid hormone. Multiple logistic regression analysis indicated that duration of renal replacement therapy was the only risk factor for the presence of ACKD (p < 0.001). There was a significant correlation between duration of renal replacement therapy and ACKD severity score (r = 0.589, p < 0.001).'] Does long-term online hemodiafiltration reduce the frequency and severity of acquired cystic kidney disease in hemodialysis patients?