Aims: To determine associations between severity of hypertension and risk of starting dialysis in the presence or absence of diabetes mellitus (DM). Methods: A nationwide database with claims data on 258,874 people with and without DM aged 19-72 y in Japan was used to elucidate the impact of severity of hypertension on starting dialysis. Initiation of dialysis was determined from claims using ICD-10 codes and medical procedures. Using multivariate Cox modeling, we investigated severity of hypertension as a predictor of the initiation of dialysis with and without DM. Results: Hypertension was significantly associated with the initiation of dialysis regardless of DM. The incidence of starting dialysis in those with SBP ≤119 mmHg and DM (DM+) was almost the same as in those with SBP ≥150 mmHg and absence of DM (DM-). In comparison with SBP ≤119 mmHg, SBP ≥150 mmHg significantly increased the risk of the initiation of dialysis about 2.5 times regardless of DM+ or DM-. Compared with DM- and SBP ≤119mmHg, the HR for DM+ and SBP ≥150 mmHg was 6.88 (95% CI 3.66-12.9). Conclusions: Although the risks of hypertension differed only slightly regardless of the presence or absence of DM, risks for the initiation of dialysis with DM+ and SBP ≤119 mmHg were equivalent to DM- and SBP ≥150 mmHg, indicating more strict blood pressure interventions in DM+ are needed to avoid dialysis. Future studies are needed to clarify the cut-off SBP level to avoid initiation of dialysis considering the risks of strict control of blood pressure.