An access port comprises a housing with a first opening and a self sealing septum sealing the first opening, the septum including an attachment portion for securing the septum to the housing, the attachment portion including a chamfer which, when the septum is mounted within the housing is subject to a force oriented substantially perpendicularly with respect to a plane of the outer surface, the chamfered portion redirecting a portion of the force to compress the outer surface. A septum for an access port comprises an attachment portion for abutting a septum seat of the access port and an operative surface permitting penetration by a needle and resealing itself after removal of the needle in combination with a chamfered portion providing a transition between the attachment portion and the operative surface, the chamfered portion re-directing a component of a force applied to the chamfered portion to compress the operative surface.