To determine whether the monitoring of patients who have undergone surgical excision of hydatid cysts of the liver is useful. Furthermore, sonographic and computertomographic criteria of recurrent hydatid disease should be described. Of 84 patients operated on for hepatic hydatid disease 42 (22 men, 20 women; mean age 44 [25-82] years) were examined between 6 months and 15 years post-operatively (median of 6 years) clinically, serologically (complement-fixation reaction, immunohaemagglutination) and by ultrasound. If the latter was positive, computed tomography was also performed. Recurrence of hydatid disease in the liver was diagnosed in three patients and in the peritoneal cavity in one patient. The demonstration of internal septa by solitary or multiple daughter cysts proved to be a reliable imaging criterion. Ultrasonography should be performed as a baseline test after surgical removal of hydatid cysts in the liver and specific antibody titres measured. This will make it easier to distinguish a recurrence from postoperative changes.