The unique versatility of medical grade silicones as tissue substitutes has stimulated an unprecedented volume of research during the past several years. This paper is presented as a summary analysis of those silicones which have proved most useful in plastic and reconstructive surgery and as a description of their physical and chemical properties, their uses and dangers. It is essential that we pause for perspective in the face of a mounting enthusiasm for the use of silicone implants. We must survey our current knowledge objectively and arrive at a sane, conservative philosophy regarding their use. The properties for ideal synthetic soft tissue well defined by Scales1 in 1953 as follows: (1) not physically modified by soft tissue, (2) chemically inert, ^3) no inflammation or foreign body reaction, (4) noncarcinogenic, (5) produces no stage of allergy or hypersensitivity, (6) capable of resisting mechanical strains, (7) capable of fabrication in the form desired and (8) capable of sterilization. Recently the various silicones have been found to have many of these properties, and hence have been used in areas that had been limited to autograft or homograft or else had been virtually untreatable. Since the silicones are relatively new, having been in existence only for the past 20 years, there is much uncertainty and lack of knowledge in the profession relative to them.