Adiponectin influences insulin sensitivity and lipid oxidation. Because low plasma adiponectin concentrations are suspected to promote atherosclerosis, we retrospectively assessed relationships of plasma adiponectin concentration to characteristics of coronary heart disease (CHD). Japanese men undergoing coronary angiography for CHD (n = 139) were grouped according to serum adiponectin concentration by enzyme-linked immunosorbent assay (low, <4.0; medium, 4.0-8; high, >8.0 microg/mL). Numbers of coronary arteries with at least 50% stenosis were determined. Serum adiponectin concentration correlated positively with age at onset of CHD (r = 0.285, P = .003). Age at CHD onset in the low-adiponectin group was younger than in the medium or high groups. Adiponectin was protective against CHD onset at ages younger than 58 years (relative risk, 0.778; P = .0047). Significantly more arteries were affected in low-adiponectin patients than in the medium or high group (each P < .01). Adiponectin concentration correlated positively with high-density lipoprotein cholesterol concentration and negatively with triglyceride concentration. Only in diabetic patients did serum adiponectin concentration correlate negatively with body mass index. Low plasma adiponectin concentrations were associated with early CHD onset and multiple atherosclerotic lesions in coronary arteries. Thus, adiponectin concentrations may influence risk of CHD and might serve as one of the screening tests facilitating early intervention.