A casing assembly for a gas turbine engine comprising: a radially inner casing; a radially outer casing; and an axial mounting arrangement (4, 4', 4") for mounting the inner casing and outer casing in a fixed axial relationship wherein the axial mounting arrangement allows radial movement of the outer casing relative to the inner casing, wherein: the outer casing has an axial extension portion which extends axially beyond the inner casing; and the casing assembly comprises mounting arrangements (4, 4', 4", 27) for connecting the radially inner casing and the radially outer casing at two and only two axial positions, the axial mounting arrangement (4, 4', 4") is provided at the more axially downstream position, characterized in that: a radial mounting arrangement is provided at the more axially upstream position, the radial mounting arrangement being for mounting the inner casing and outer casing in a fixed radial relationship whilst allowing axial movement of the inner casing relative to the outer casing; and the axial mounting arrangement comprises either a radially inwards-directed annular flange depending from the outer casing and a circumferential groove provided on said inner casing or a radially outwards-directed annular flange extending from the inner casing and a circumferential groove provided on said outer casing, wherein the circumferential groove receives said annular flange and wherein the annular flange is radially slidable within said groove. a radially inner casing; a radially outer casing; and an axial mounting arrangement (4, 4', 4") for mounting the inner casing and outer casing in a fixed axial relationship wherein the axial mounting arrangement allows radial movement of the outer casing relative to the inner casing, wherein: the outer casing has an axial extension portion which extends axially beyond the inner casing; and the casing assembly comprises mounting arrangements (4, 4', 4", 27) for connecting the radially inner casing and the radially outer casing at two and only two axial positions, the axial mounting arrangement (4, 4', 4") is provided at the more axially downstream position, characterized in that: a radial mounting arrangement is provided at the more axially upstream position, the radial mounting arrangement being for mounting the inner casing and outer casing in a fixed radial relationship whilst allowing axial movement of the inner casing relative to the outer casing; and the axial mounting arrangement comprises either a radially inwards-directed annular flange depending from the outer casing and a circumferential groove provided on said inner casing or a radially outwards-directed annular flange extending from the inner casing and a circumferential groove provided on said outer casing, wherein the circumferential groove receives said annular flange and wherein the annular flange is radially slidable within said groove. a radial mounting arrangement is provided at the more axially upstream position, the radial mounting arrangement being for mounting the inner casing and outer casing in a fixed radial relationship whilst allowing axial movement of the inner casing relative to the outer casing; and the axial mounting arrangement comprises either a radially inwards-directed annular flange depending from the outer casing and a circumferential groove provided on said inner casing or a radially outwards-directed annular flange extending from the inner casing and a circumferential groove provided on said outer casing, wherein the circumferential groove receives said annular flange and wherein the annular flange is radially slidable within said groove.