Although simple renal cysts are thought to be related to hypertension, no reports have examined the relationship between simple renal cysts and prehypertension. Here, we evaluated the effects of simple renal cysts on prehypertension and hypertension and the role of serum renin levels in the cyst-related prehypertension/hypertension in adults. A total of 14,995 patients were enrolled and divided into normotension, prehypertension, and hypertension groups. Simple renal cysts were classified into different categories based on number (1 vs. ≥ 2 cm) and size (<2 vs. ≥ 2 cm). In multivariate analysis, simple renal cysts were independently related to prehypertension/hypertension. Two or more simple renal cysts or cyst of ≥ 2 cm were independently associated with prehypertension/hypertension. However, the association between cyst of ≥ 2 cm and prehypertension/hypertension disappeared after further adjusting for serum renin level in an exposure-matched subgroup analysis. Thus, the presence of two or more simple renal cysts and cyst of ≥ 2 cm were the important determinants of prehypertension and hypertension in adults. One possible mechanism of cyst-related prehypertension/hypertension may be related to an increased serum renin level. We recommend close monitoring of blood pressure routinely among patients with two or more simple renal cysts.