Wistar rats were used to study the effects, if any, of membrane thickness and implant volume of a silicone gel prosthesis on the development of fibrous capsule contraction. A total of 30 miniprosthesis with three different membrane thicknesses and two different volumes were implanted in the subcutaneous space of five animals. One hundred eighty days later the fibrous capsule was resected and histologically analyzed. Different grades of thickness were observed. The statistical analysis of the data indicates that the thickness of the prosthesis' membrane and the implant's volume did not impact significantly on the grade of fibrosis.