The objective of this study was to determine the site-specific cancer incidence of hypertensive patients and examine the effect of blood pressure-related variables on the risk of cancers with elevated incidence among the hypertensive patients. A record linkage study of Hypertension Register of the North Karelia Project and the Finnish Cancer Registry was conducted. The mean follow-up time was 16 years. A total of 20 529 hypertensive patients were studied. Main outcome measures were standardised incidence ratios and hazard ratios. The overall cancer incidence was close to that of the general population for both men and women. The incidence rate for the kidney cancer was significantly increased in hypertensive patients (standardised incidence ratio 1.34, 95% confidence interval (CI) 1.11-1.60), as well as incidence rates for cancers of pancreas (1.26, 1.02-1.54), and endometrium (1.22, 1.01-1.44) in hypertensive women. The incidence of lung cancer was significantly decreased (0.86, 0.77-0.95). The incidence of liver cancer was elevated with borderline significance (1.36, 0.99-1.82). In Cox regression models, the use of antihypertensive drugs at baseline was a significant predictor of kidney (hazard ratio for use of antihypertensive drugs 1.89, 95% CI 0.96-3.75) and pancreatic cancer (1.78, 0.99-3.22) in women but not in men. The incidence of endometrial cancer or liver cancer was not related to blood pressure levels or the use of antihypertensive drugs. In women, obesity was a significant predictor of cancers of the endometrium, kidney and liver. In conclusion, increased occurrence of some cancer types among hypertensive patients seem to be partly explained by obesity and the use of antihypertensive drugs.