OBJECTIVE - To test at the population level whether people with multiple metabolic syndrome (MMS) disorders have reduced cardiac autonomic activity (CAA). RESEARCH DESIGN AND METHODS - We examined the association between the level of CAA and MMS disorders, at the degree of clustering and the segregate combination levels, using a random sample of 2,359 men and women aged 45-64 years from the biracial, population-based Atherosclerosis Risk in Communities (ARIC) Study. Supine resting 2-min beat-to-beat heart rate data were collected. High-frequency (HF) (0.15-0.35 Hz) and low-frequency (LF) (0.025- 0.15 Hz) spectral powers, the ratio of LF to HF, and the SD of all normal R- R intervals (SDNN) were used as the conventional indices of heart rate variability (HRV) to measure CAA. The MMS disorders included hypertension, type 2 diabetes, and dyslipidemia. RESULTS - HRV indices were significantly lower in individuals with MMS disorders. The multivariable adjusted mean HF was 0.85 (beat/min)2 in subjects with all three MMS disorders, in contrast to 1.31 (beat/min)2 in subjects without any MMS disorder. At the segregated combination level, the multivariable adjusted means ± SEM of HF were 1.34 ± 0.05, 1.16 ± 0.05, 1.01 ± 0.17, and 1.34 ± 0.05 (beat/min)2, respectively, for subjects without any MMS disorder, with hypertension only, with diabetes only, and with dyslipidemia only, and the means ± SEM of HF were 0.93 ± 0.04, 0.70 ± 0.15, and 1.20 ± 0.05 (beat/min)2, respectively, for subjects with diabetes and hypertension, diabetes and dyslipidemia, and hypertension and dyslipidemia. An increase in fasting insulin of 1 SD was associated with 88% higher odds of having a lower HF. The pattern of associations was similar for LF and SDNN. CONCLUSIONS - These findings suggest that MMS disorders adversely affect cardiac autonomic control and a reduced cardiac autonomic control may contribute to the increased risk of subsequent cardiovascular events in individuals who exhibit MMS disorders.