The authors report three cases of calcified renal cysts containing blood. The discovery was made by chance on straight X ray of the abdomen. It gives a round image, finely calcified, its position is not always obvious, especially when it develops forewards. Whether it deforms or not the urinary tract, this echogenic mass on echotomography, is avascular on arteriography. As all renal diseases, cysts, tumours, vascular anomalies, dysplasias, infections, may become calcified, the diagnosis is not always easy. The absence of central calcifications, and the purely peripheral position of the calcifications limits the discussion to three differential diagnoses when the mass is peripheral: carcinoma of the kidney, hydatid cyst, and calcified cyst containing blood. The parasitic immunological reactions and renal arteriography should lead to the diagnosis. When in doubt, surgical exploration is indicated. It permits kystectomy and pathological examination.