Thyroid dysfunction has long been reported in patients with liver disease, but limited information is available on thyroid gland size in cirrhosis. Most studies were carried out on small, selected series of patients, and no study has measured thyroid volume in relation to the etiology of liver disease. Thyroid volume was measured at ultrasound in 118 consecutive patients with cirrhosis of different etiology and 48 healthy subjects matched for age and sex. No subjects had evidence of overt thyroid disease. The mean volume was increased by 17% (from 16.0 [SD 5.2] ml in controls to 18.8 [7.6] in cirrhosis; P less than 0.025), and thyroid enlargement (antero-posterior diameter greater than 20 mm) was present in 38% of cases, in the presence of hormone values indicative of low-T3 syndrome. No significant differences in thyroid gland size were observed in relation to the extent of liver dysfunction or to the etiology of liver disease. The prevalence of thyroid nodules was similar in controls and in patients with cirrhosis. In only 8% of cases were laboratory values indicative of hypothyroidism, with low free triiodothyronine and raised thyroid-stimulating hormone levels; in these patients thyroid volume was decreased on average by 26%. This was mainly the case with patients with primary biliary and alcoholic cirrhosis. The largest mean thyroid volume was observed in patients with HBsAg + ve postnecrotic cirrhosis, whose thyroid volume was increased on average by 37%, and 53% of subjects had thyroid enlargement. This finding raises the question of a possible direct involvement of the thyroid in hepatitis B virus infection.