PURPOSE. The venous choroidal blood drains through the superior orbital vein into the intracranial cavernous sinus. The cerebrospinal fluid pressure (CSFP) may thus influence the choroidal venous blood pressure. Since volume and thickness of the choroid depend on its pressure, we tested the hypothesis whether the subfoveal choroidal thickness (SFCT) is associated with CSFP. METHODS. The population-based Beijing Eye Study 2011 included 3468 individuals. A detailed ophthalmic examination was performed including spectral-domain optical coherence tomography (SD-OCT) with enhanced depth imaging for measurement of SFCT. The CSFP was calculated as CSFP (mm Hg) 0.44 x Body Mass Index (kg/m(2)) + 0.16 3 Diastolic Blood Pressure (mm Hg) - 0.18 3 Age (years) - 1.91. RESULTS. Mean calculated CSFP was 8.8 +/- 3.7 mm Hg and mean SFCT was 254 6 107 mu m. In multivariate analysis, SFCT was significantly associated with higher CSFP (P 0.009; standardized coefficient beta: 0.08; regression coefficient B: 2.27) after adjusting for lower age (P < 0.001; beta: 0.36; B: 3.99), shorter axial length (P < 0.001; beta: 0.37; B: 35.7), lower body mass index (P = 0.02; beta: -0.05; B: -1.51), and higher corneal curvature radius (P < 0.001; beta: 0.10; B: 41.1). In univariate analysis, SFCT increased by 9.2 mu m (95% confidence interval: 8.3, 10.1) for each mm Hg increase in CSFP. In a reverse manner, CSFP was significantly associated with thicker SFCT (P < 0.001; B: 0.007; beta: 0.21), after adjusting for region of habitation (P < 0.001; B: -0.31; beta: -2.32), higher levels of glucose (P = 0.02; B: 0.10; beta: 0.04) and triglycerides (P < 0.001; B: 0.13; beta: 0.09), higher intraocular pressure (P < 0.001; B: 0.17; beta: 0.12), and thinner lens (P < 0.001; B: -2.39; beta: -0.22). CONCLUSIONS. Thicker subfoveal choroid was associated with higher CSFP after adjustment for age, axial length, body mass index, and corneal curvature radius. This association may explain thicker SFCT measurements in the morning than evening. It shows the importance of the CSFP for the physiology of the eye.