Isolated diastolic hypertension (IDH) is a largely underrated risk factor for cardiovascular disease (CVD). It is currently unclear whether a reduction in blood pressure (BP) is associated with CVD events among adults with IDH. We aimed to elucidate the relationship between BP reduction and incident CVD in individuals with IDH. We retrospectively analysed the data of 71 297 individuals with IDH. Isolated diastolic hypertension was defined as systolic BP of < 140 mmHg and diastolic BP (DBP) of ≥90 mmHg (median age, 48 years; 83.1% men; median DBP, 92 mmHg). None of the participants took BP-lowering medications or had a history of CVD at baseline. Blood pressure was measured at baseline and 1-year follow-up, and participants were categorized into two groups based on DBP at 1 year (≥90 or < 90 mmHg). The primary outcome was a composite endpoint that included myocardial infarction, stroke, and all-cause death. Over a mean follow-up period of 1100 ± 859 days, 1317 composite CVD endpoints were recorded. Participants with DBP of < 90 mmHg at 1 year were at a lower risk of composite CVD events [hazard ratio (HR): 0.75, 95% confidence interval (CI): 0.67-0.83] than those with DBP of ≥90 mmHg at 1 year. A reduction in DBP per 5 mmHg during the 1-year follow-up was associated with a lower composite CVD event risk (HR: 0.92, 95% CI: 0.89-0.95). The results remained consistent across a multitude of sensitivity analyses. Our analysis of a large-scale epidemiological dataset demonstrated a relationship of reduction in DBP with a reduced risk for CVD events in individuals with IDH.