Long-term observation of the use-effectiveness and safety of 745 Copper-IUD's has demonstrated: 1) The pregnancy rate decreases distinctly after 2 years; until now no pregnancy has been observed after 4 years continuous use. 2) The endometrium responds first with an inflammatory reaction, later it shows signs of deficient secretion, but after a longer period seems to become normal again. 3) Contamination of IUD's begins early, mostly with bacteria of vaginal origin, later the number of sterile IUD's increases. -- A septic abortion after pregnancy with an IUD in situ has not occurred amongst our cases. 4) The rate of copper elution continues steadily, but in spite of demonstrable corrosion there is no obse-vable decrease of contraceptive effectiveness. Copper-IUD's can remain as long as 5 years in situ, if no untoward side effects (pain, bleeding, infection) occur. It may be advisable to remove them after that period as corrosion may affect devices at present commercially available.