In this communication data on the natural history of euthyroid multinodular goitres are presented. From a total group of 140 patients (mean age 54.6 years, 14 men and 126 women; 88 with autonomous, 52 with non-autonomous function), follow-up data were available for 90 patients (mean age 54.0 years, 11 men and 79 women; 64 with autonomous, 26 with non-autonomous function). During follow-up (means: 5.0 years, maximum 12.2 years) transitions in function were seen 15 times; 8 autonomous patients became hyperthyroid after less than 1-7 years. There were 6 transitions from non-autonomy to autonomy and 1 from autonomy to non-autonomy. One patient who demonstrated the whole cycle from non-autonomy through autonomy up to hyperthyrodism is described in more detail. In one patient operated upon because of hyperparathyroidism a follicular carcinoma was found by chance. Mechanical problems were the reason for surgery in 6 patients only, 16 patients were operated upon because of cosmetic reasons (mostly in the early years of the study). Finally, results from 19 TRH tests in 16 autonomous patients suggest that TRH tests in patients with autonomously functioning euthyroid multinodular goitres are not yet redundant.