To determine the nature and course of cystic pancreatic lesions, we reviewed the records of 93 patients who were followed up with serial ultrasound until resolution occurred or definitive therapy was given. Initially, 105 cystic lesions were seen. Single cysts occurred in 83 patients and multiple cysts in ten. Eight patients had two cysts and two patients had three. Twenty-one patients had a single ultrasound examination and 72 had two or more examinations. Spontaneous resolution occurred in 29 of (28%) 105 cysts in 24 patients. In 46 patients, 53 pseudocysts were found at operation or autopsy. Five patients had pancreatic abscesses. Two patients became unavailable for follow-up and three refused surgery. The results of one examination were false negative. Twelve patients had false-positive ultrasound results. Factors influencing the likelihood of spontaneous resolution included initial cyst size, subsequent increase in size, multiple cysts, and the presence of calcifications. This study confirms the usefulness of serial ultrasound scans in determining the nature and necessity for treatment of cystic lesions of the pancreas.