Background No longitudinal study compared associations of echocardiographic indexes of diastolic left ventricular function studies with conventional ( CBP ) and daytime ambulatory ( ABP ) blood pressure in the general population. Methods and Results In 780 Flemish (mean age, 50.2 years; 51.7% women), we measured left atrial volume index ( LAVI ), peak velocities of the transmitral blood flow (E) and mitral annular movement (e′) in early diastole and E/e′ 9.6 years (median) after CBP and ABP . In adjusted models including CBP and ABP , we expressed associations per 10/5‐mm Hg systolic/diastolic blood pressure increments. LAVI and E/e′ were 0.65/0.40 mL/m ² and 0.17/0.09 greater with higher systolic/diastolic ABP ( P ≤0.028), but not with higher baseline CBP ( P ≥0.086). e′ was lower ( P ≤0.032) with higher diastolic CBP (−0.09 cm/s) and ABP (−0.19 cm/s). When we substituted baseline CBP by CBP recorded concurrently with echocardiography, LAVI and E/e′ remained 0.45/0.38 mL/m ² and 0.15/0.08 greater with baseline ABP ( P ≤0.036), while LAVI (+0.53 mL/m ² ) and E/e′ (+0.19) were also greater ( P <0.001) in relation to concurrent systolic CBP . In categorized analyses of baseline data, sustained hypertension or masked hypertension compared with normotension or white‐coat hypertension was associated with greater LAVI (24.0 versus 22.6 mL/m ² ) and E/e′ (7.35 versus 6.91) and lower e′ (10.7 versus 11.6 cm/s; P ≤0.006 for all) with no differences ( P ≥0.092) between normotension and white‐coat hypertension or between masked hypertension and sustained hypertension. Conclusions ABP is a long‐term predictor of diastolic left ventricular function, statistically outperforming distant but not concurrent CBP . Masked hypertension and sustained hypertension carry equal risk for deterioration of diastolic left ventricular function.