The crystallized mineral deposits on 91 copper IUDs removed by normal procedures were analyzed using x-ray diffraction. 50 Nova-T, 27 Multiload 375, and 14 Gravigard devices were divided into a group of 32 in place for 10-36 months and a group of 59 in place for over 36 months. Studies were performed by x-ray diffraction on whole IUDs in the fresh or dry state and by using classic x-ray, infrared, and atomic absorption spectrometry methods on deposits. Coils of all the IUDs were covered with a layer of cuprous oxide adherent to the metal that flaked over time. Crystals or coatings formed white deposits on 63% of all IUDs, especially when cuprous oxide adhered to the metal. The deposits covered 65-85% of adherent oxides and only 33-38% of flaked oxides for the 1st and 2nd durations of use respectively. Deposits were more abundant on Nova T and Gravigard than on Multiload devices. For the short and long periods of use, the respective frequencies were 67 and 74% on Nova Ts, 25 and 47% on Multiloads, and 88 and 67% on Gravigard. Calcium carbonate (CaCO3) was the only crystalline inorganic compound found, and was present with or without white deposit on 80% of IUDs. It was in the form of calcite, accompanied by vaterite in 40% of cases and rarely by aragonite. Calcium was substituted by magnesium, with an average of 3.7 atoms. Sodium, potassium, and excess magnesium were not in the organic crystalline phase.