Over a 10-year period, nine patients (four men, five women, mean age 27 years) underwent surgery for splenic cysts (six epidermoid cysts, two mesothelial cysts and one pseudocyst). Six patients had had suggestive clinical symptoms, but, in the other three, the cysts were only discovered by chance on ultrasound scan. Three of the patients with epidermoid cysts had raised serum concentrations of the tumour markers carcinoembryonic antigen (CEA) or carbohydrate antigen (CA 19-9. All six benign epidermoid cysts contained immunohistochemically demonstrable CEA and/or CA 19-9 in the inner epithelial layer, implying a mesothelial origin for these cysts. In five cases the splenic cysts were completely extirpated (splenectomy in two, hemisplenectomy in one, enucleation in two); in four cases cyst resection was performed, leaving part of the cyst adherent to the spleen. In one of these four patients, a 4 cm cyst persisted postoperatively in the hilus of the spleen, but has remained unchanged over an 8-year period. Splenic cysts are usually benign, despite the presence of tumour markers in the cyst wall, and do not require removal. The only indications for surgical intervention are complications (e.g. rupture), symptomatic cysts or asymptomatic cysts with an increased risk of rupture (diameter greater than 5 cm). The very rare parasitic and infective forms must always be surgically sterilized.