The invention relates to a mixing device (10) for mixing a first substance and a second substance which are provided in a first or second container. The mixing device comprises a first adapter (12) with a circumferential wall (47), which is suitable for receiving the first container and along which a cannula body (64) runs that is at least partly surrounded by the circumferential wall, and with a hollow cylindrical portion (26), which is connected to the cannula body. The mixing device also comprises a second adapter (14) with a circumferential wall, which is suitable for receiving the second container and along which a cannula body (164) runs that is at least partly surrounded coaxially by the circumferential wall, and with a hollow cylindrical portion (126), which is connected to the cannula body. In the connected state of the first and second adapter, the hollow cylindrical portions engage into each other preferably in a fluid-tight manner, and the first and second adapter can be screwed together in a releasable manner. The invention is characterized in that the first and second adapter (12, 14) each has a hollow cylindrical outer body (16, 18) with an outer circumferential wall (32, 132) and an intermediate wall (24, 124) which runs perpendicular to the longitudinal axis of the outer body； a portion (128), which has an inner thread (134), of the outer circumferential wall of one adapter surrounds a portion (28), which has an outer thread (34), of the outer circumferential wall of the other adapter when the threaded portions are engaged together in the connected state of the adapters； and the hollow cylindrical outer body of the first and/or the second adapter has an insert (46, 146) comprising the circumferential wall (47, 147) which receives the first or second container.
