Incidence of renal hydatid cyst is rare and its diagnosis should be made with the utmost care and after subjecting the patient to intensive investigations to exclude other pathologies. Because of the rarity of the disease and because of the clinical similarity with other surgical lesions affecting the kidney, mainly renal tumours and simple renal cysts, the authors are encouraged to record thirty-nine cases of renal hydatid cysts. The value of investigations as aids in the diagnosis has been discussed. The direct consequence of uncertain diagnosis is the risk of performing unwarranted ablative surgery, whereas conservative treatment is currently advocated by the majority of investigators. We followed the policy of saving as much renal tissue in each case, and we obtained results that encourage us to believe that nephrectomy for renal hydatidosis can be avoided in a great many cases with complete therapeutic success. With the exception of cystectomy and marsupialisation--which is recommended as a lifesaving procedure, the method of our choice consisted of a partial pericystectomy, i.e. resection of the pericystium exteriorized until it was flush with the renal parenchyma.