Study Objectives: The association of mild obstructive sleep apnea (OSA) with important clinical outcomes remains unclear. We aimed to investigate the association between mild OSA and systemic arterial hypertension (SAH) in the European Sleep Apnea Database cohort. Methods: In a multicenter sample of 4,732 participants, we analyzed the risk of mild OSA (subclassified into 2 groups: MildAHI 5-<11/h (apnea-hypopnea index [AHI], 5 to <11 events/h) and mildAHI 11-<15/h (AHI, .11 to <15 events/h) compared with nonapneic snorers for prevalent SAH after adjustment for relevant confounding factors including sex, age, smoking, obesity, daytime sleepiness, dyslipidemia, chronic obstructive pulmonary disease, type 2 diabetes, and sleep test methodology (polygraphy or polysomnography). Results: SAH prevalence was higher in the mildAHI 11-<15/h OSA group compared with the mildAHI 5-<11/h group and nonapneic snorers (52% vs 45% vs 30%; P < -001). Corresponding adjusted odds ratios for SAH were 1.789 (mildAHI 11-<15/h; 95% confidence interval [CI], 126.96.36.199) and 1.558 (mildAHI 5-<11/h; 95%, CI, 188.8.131.52), respectively (P <.001). In sensitivity analysis, mildAHI 11-<15/h OSA remained a significant predictor for SAH both in the polygraphy (odds ratio, 1.779; 95% CI, 1.403.2.256; P < -001) and polysomnography groups (odds ratio, 1.424; 95% CI, 1.047.1.939; P = .025). Conclusions: Our data suggest a dose-response relationship betweenmild OSA and SAH risk, starting from 5 events/h in polygraphy recordings and continuing with a further risk increase in the 11-to <150-events/h range. These findings potentially introduce a challenge to traditional thresholds of OSA severity and may help to stratify participants with OSA according to cardiovascular risk.