Diastolic dysfunction (DD), an abnormality in cardiac left ventricular (LV) chamber compliance, is associated with increased morbidity and mortality. Although DD has been extensively studied in older populations, co-morbidity patterns are less well characterized in middle-aged subjects. We screened 156,434 subjects with transthoracic echocardiogram reports available through Vanderbilt's electronic heath record and identified 6,612 subjects 40 to 55 years old with an LV ejection fraction ≥50% and diastolic function staging. We tested 452 incident and prevalent clinical diagnoses for associations with early-stage DD (n = 1,676) versus normal function. There were 44 co-morbid diagnoses associated with grade 1 DD including hypertension (odds ratio [OR] = 2.02, 95% confidence interval [CI] 1.78 to 2.28, p <5.3 × 10−29), type 2 diabetes (OR 1.96, 95% CI 1.68 to 2.29, p = 2.1 × 10−17), tachycardia (OR 1.38, 95% CI 0.53 to 2.19, p = 2.9 × 10−6), obesity (OR 1.76, 95% CI 1.51 to 2.06, p = 1.7 × 10−12), and clinical end points, including end-stage renal disease (OR 3.29, 95% CI 2.19 to 4.96, p = 1.2 × 10−8) and stroke (OR 1.5, 95% CI 1.12 to 2.02, p = 6.9 × 10−3). Among the 60 incident diagnoses associated with DD, heart failure with preserved ejection fraction (OR 4.63, 95% CI 3.39 to 6.32, p = 6.3 × 10−22) had the most significant association. Among subjects with normal diastolic function and blood pressure at baseline, a blood pressure measurement in the hypertensive range at the time of the second echocardiogram was associated with progression to stage 1 DD (p = 0.04). In conclusion, DD was common among subjects 40 to 55 years old and was associated with a heavy burden of co-morbid disease.