This study was carried out to investigate the clinical and biochemical factors which might be of importance in predicting the outcome of patients with myxoedema coma. Eleven patients (ten female) aged 68·1 19·5 years attended our institution over a period of 18 years.Glasgow and APACHE II scores and serum free thyroxine and TSH were measured in all the patients on entry. Patients were selected at random to be treated with two different regimens of -thyroxine.Four patients died with the mortality rate being 36·4%. The patients in coma at entry had significantly higher mortality rates than those with minor degrees of consciousness (75% vs 14·3% respectively, P=0·04). The surviving patients had significantly higher Glasgow scores than those who died (11·85 2·3 vs 5·25 2·2 respectively, P,0·001). Comparison of the mean values of APACHE II scores between the surviving group and those who died was significantly different (18·0 2·08 vs 31·5 2·08 respectively, P,0·0001).The degree of consciousness, the Glasgow score and the severity of the illness measured by APACHE II score on entry were the main factors that determined the post-treatment outcome of patients with myxoedema coma.