Ten specimens of adrenal cyst resected during the period 1984-1999 were re-examined. Thorough examination of multiple sections and the use of immunohistochemistry allowed to change the recorded diagnosis in 8 cases: three epithelial cysts and five pseudocysts were redefined as endothelial cysts. All 10 cysts were of the endothelial type. A synthetic review of the current knowledge about the pathogenesis, the classification and the clinical aspects of this rare disease is presented.