Abstract: The invention relates to an implantable medical device for injecting and/or collecting fluid substance into and/or from a human or animal organism, said device comprising a casing (6) whose wall (3) delimits a chamber and is pierced with at least a first access orifice (7) designed to allow a needle to pass through said wall (3), said device being characterized in that the first access orifice has a staged structure comprising: a guide portion designed to limit the angular clearance of the needle when said needle is engaged therein, and a flared intake portion that forms a continuation of the guide portion, so as to be able to cause the trajectory of the incoming needle to converge on the guide portion. Implantable medical devices.