The osmotic tissue expander is a new device made of a hydrogel expanding skin that does not require external fillings. Once implanted, it absorbs body fluids, which leads to a gradual swelling of the device. The swelling phase is completed in 6 to 8 weeks and results in skin gain. Different shapes and sizes are available, and the devices can be used in almost every area of the body. Over a 4-year period, the osmotic tissue expander was used in 58 patients in different areas of the body. A round osmotic tissue expander was mainly used in breast reconstruction, and a rectangular expander was used for defect coverage after excision (i.e., of scars and tumors). The mean age of the patients was 49.34 years (range, 4 to 76 years). During the expansion phase, the patients noted only a little discomfort and pain for the first few days. Without a silicone membrane in the first-generation expander, the rate of successful explantation and good final result was 81.5 percent. In a few cases, rapid swelling of the device led to the introduction of a silicone membrane that encloses the expander and leads to a slower, more gradual, and consistent swelling. After introduction of the silicone envelope, the success rate improved to 91 percent. The expander is now used with a silicone membrane in every case. The osmotic tissue expander has many advantages compared with the conventional expander: there is no need for painful external fillings and the risk of external infections is avoided. The expander is 10 percent of its final volume and only requires a short incision and a small pocket. An operation can easily be performed under local anesthesia, with minimal tissue mobilization in older children and compliant patients.