Abstract Aims Aortic valve calcification in aortic sclerosis, a precursor of aortic stenosis (AS), is not always present in all three leaflets; how calcification develops in each leaflet is unknown. We aimed to investigate the natural history of calcification development in each aortic valve leaflet and the prognostic value of the number of calcified leaflets. Methods and results In a retrospective multicentre cohort study of patients undergoing haemodialysis without AS, we observed calcification development in each aortic valve leaflet using echocardiography. We investigated the association between the number of calcified leaflets and AS development and mortality using time-to-event analysis. Among the 1507 patients (mean age, 66 years; 66% male) included in the longitudinal echocardiography analysis, 709 (47%) had aortic sclerosis at baseline: one-leaflet calcified, 370 (52%); two-leaflet calcified, 215 (30%); and three-leaflet calcified, 124 (17%). The median time for one calcified leaflet increase was 3–4 years, and 251 (17%) patients developed AS during a median 3.2-year follow-up. The increased number of calcified aortic valve leaflets was associated with developing AS; compared with that of one-leaflet calcified, the adjusted hazard ratios (aHRs) 95% confidence intervals (CIs) of two- and three-leaflet calcified were 2.12 (1.49–3.00) and 4.43 (3.01–6.52), respectively; the aHR (95% CI) per one calcified leaflet increase was 2.24 (1.96–2.55). It was also associated with all-cause mortality; the aHR (95% CI) per one calcified leaflet increase was 1.18 (1.08–1.27). Conclusion The number of calcified aortic valve leaflets strongly predicted AS development and even mortality in patients undergoing haemodialysis, suggesting the usefulness of assessing calcification for each valve leaflet separately using echocardiography. Graphical Abstract Graphical Abstract Aortic valve calcification in patients undergoing haemodialysis typically progresses by one leaflet within 3–4 years, and aortic stenosis (AS) develops approximately 4 years after all three leaflets are calcified. The number of calcified aortic valve leaflets is a predictor of AS development and all-cause mortality.