Background and Aims: Although the importance of hypertension in patients with cancer is widely recognized, little is known about the risk of developing hypertension in patients with a history of cancer. Methods: This retrospective observational cohort study analyzed data from the JMDC Claims Database between 2005 and 2022, including 78,162 patients with a history of cancer and 3,692,654 individuals without cancer. The primary endpoint was the incidence of hypertension. Results: At the initial health check-up, the median systolic and diastolic blood pressure were 116 (IQR:106-126) and 71 (IQR:64-80) mmHg. The median age of the study participants was 43 years (IQR, 35-51 years), and 2,118,101 (56.2%) were men. During a mean follow-up period of 1,208 ± 966 days, 311,197 participants developed hypertension. Compared to individuals without a history of cancer, the cumulative incidence of hypertension was higher in individuals with a history of cancer (log-rank test, P<0.001). The incidence of hypertension was 364.6 (95% CI 357.0-372.2) per 10000 person-years among those with a history of cancer and 247.2 (95% CI 246.3-248.1) per 10000 person-years in those without cancer. Individuals with a history of cancer had an elevated risk of developing hypertension according to multivariable Cox regression analyses (HR 1.17, 95% CI 1.15-1.20). Both cancer patients requiring active chemotherapy (HR 2.01, 95% CI 1.85-2.20) and those who did not require active chemotherapy (HR 1.14, 95% CI 1.12-1.17) had an increased risk of hypertension. A multitude of sensitivity analyses confirmed the robustness of the relationship between cancer and incident hypertension. Patients with certain types of cancer were found to have a higher risk of developing hypertension than those without cancer, with varying risks dependent on the types of cancer. Conclusions: Our analysis of a nationwide epidemiological dataset revealed that individuals with a history of cancer have a higher risk of developing hypertension, and that this finding applies to both cancer patients who require active chemotherapy and those who do not. The results of this study confirm the importance of the novel scientific field of "onco-hypertension”.