Recurrent calculi of the main bile way may be recurrent or residual. Recurrent stones are yellow-brown, crumbly and earthy and contain high quantities of calcium palmitate; residual stones, on the other hand, are firmer, round or berry-like, usually faceted and contain cholesterol, bilirubinate and carbonate of calcium (aragonite, vaterite, etc.) but never palmitate. Residual stones at times also present a peripheral "shell" presenting palmitate and this shows that a new component determined by bile changes is added to the cholesterol stone, which represents the central core, because of stasis and biliary infection. The distinction of calculi into residual and recurrent is also made on the basis of the classic morphologic and clinical criteria described in the literature, also and above all on the basis of specific, objective scientific criteria deriving from in-depth clinical study of the patient, the chemical study of the bile, morphological, mineralogical and structural study of the stone. The following are considered in particular: instrumental examinations made during hospitalisation and operation; pH, enzymatic activity (phospholipase, trypsin and amylase) and examination of bile cultures; morphological, microscopic examination (electronic scan microscopy) and mineralogical examination (X-ray diffractometry and infrared spectroscopy) of the calculus. A personal series of recurrent calculosis of the main biliary way is considered, special attention being paid to a case that was particularly interesting in relation to the fact lithiasic recurrence occurred just 10 months after the previous operation and the fact that biliary stasis was not determined by stenosis of the papilla which proved fully patent.