Objective: Study of the dimensional stability of three addition silicones after steam autoclave sterilization. Material and Methods: For this study, addition silicones were used in an automatic mixing machine, Pentamix 2 (3M ESPETM): Express Penta H (3M ESPETM), Affinis System 360 (Coltène/Whaledent), Aquasil Ultra Heavy Regular - Smart Wetting Impression Material (Dentsply). Six groups were formed. Groups 1, 2 and 3 followed a protocol of chemical disinfection with sodium hypochlorite 5.25% for 10 minutes. Groups 4, 5 and 6 were submitted to the same disinfection followed by autoclaving at 134°C for 25 minutes. The samples were obtained with a metallic matrix from ADA Specification n°19 and ISO 4823:2000. The measurements were taken right after obtaining the samples, after the applied procedures, 24 hours later, two weeks later and six months later. Two lines were measured in each sample, line A and line B. Results: The Aquasil Ultra Heavy Regular - Smart Wetting Impression Material (Dentsply) had the lowest dimentional modification, in contrast with the Express Penta H (3M ESPETM) which had the highest values of dimensional changing. Conclusion: The studied addition silicones have showed dimensional changes. However, the ADA Specification n°19 (1977) established that these changes aren't significant for they don't exceed 0,5%. In this study, addition silicones didn't suffer significant dimensional changes after autoclaving. Keywords: dimensional stability, addition silicones, sterilization