a coupling device for medical purposes with at least one coupling channel having a mouth in a coupling surface , for sealed co - operation with at least one access channel with a mouth in a connecting surface . of an access device , which is connectable to a patient , is distinguished in that the coupling surface includes a flexible portion for contacting against the connecting surface and being of a material having a higher degree of flex than a primary material of the coupling device , which portion for sealing purposes surrounds the mouth of said at least one coupling channel .