Abstract The development of the hydrogelic occlusive device called the P-block is described including developmental steps of the design of the device as well as the experience gained concerning the hydrogel of the device, shelf life, animal and human toxicology, insertion techniques, analgesia, check-up for retention in situ, actual efficiacy of the method, mode of action of the device, complication rates, patient acceptance, continuation rates, possible reversibility and future perspectives of the method. Over a period of 10 years more than 900 woman years were observed. The gross Pearl Index for the total series of nine different designs of P-blocks is 5, due to rejection of the device on either or both sides. The corresponding value for intact P-blocks in situ is 0.3. With the latest version of P-blocks — Mark 9 — a total of 191 women have been observed over 637 woman years during a mean of 21 months with a maximum time of observation of 88 months in the single case. The continuation rate, when no pregnancy occurs is 99% over 10 years. After unilateral expulsion and intra-uterine pregnancy 48% return for reinsertion of P-blocks. The rate of complications, including extra-uterine pregnancies was neglectable as was the loss for follow-up. Life table analysis revealed that no pregnancy occurred after 30 months from the insertion of P-blocks.