Overt hypothyroidism may result in accelerated atherosclerosis and coronary heart disease (CHD) presumably because of the associated hypertension, hypercholesterolemia, and hyperhomocysteinemia. As many as 10%-15% of older women have subclinical hypothyroidism (SH) and thyroid autoimmunity. Whether SH is associated with risk for CHD is controversial. We examined 57 women with SH and 34 healthy controls. SH was defined as an elevated thyrotropin (TSH) (>4.5 mU/L) and normal free thyroxine (FT(4)) level (8.7-22.6 nmol/L). None of the patients had been previously treated with thyroxine. In all participants we determined blood pressure, body mass index (BMI), and fasting TSH, FT(4), antibodies to thyroid peroxidase and thyroglobulin, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides, folic acid, vitamin B(12), creatinine, and total plasma homocysteine levels. The SH and control groups did not differ in their total homocysteine values. Mean diastolic blood pressure was increased in SH patients versus controls (82 vs. 75 mm Hg; p < 0.01). Mean values of TC, HDL-C, LDL-C, triglycerides, TC/HDL-C, and LDL-C/HDL-C were not different in patients with SH compared with controls. Individual analysis revealed that the percentage of patients with SH having hypertension (20%), hypertriglyceridemia (26.9%), elevated TC/HDL-C (11.5%), and LDL-C/HDL-C (4%) ratios were higher than the percentages in controls. Hyperhomocysteinemia (> or = 10.98 micromol/L) was observed in 29.4% of SH and was not significantly different from the percentage in controls (21.4%). No significant correlation between TSH and biochemical parameters was detected. We conclude that subclinical hypothyroidism in middle-aged women is associated with hypertension, hypertriglyceridemia, and elevated TC/HDL-C ratio. This may increase the risk of accelerated atherosclerosis and premature coronary artery disease in some patients.