The invention relates to an expandable socket (1) for a hip joint endoprosthesis able to be cementlessly anchored in place which is at least approximately hemispherical and which is provided with a plurality of slots (3) extending in a meridional direction, thus forming intervening tongues (4), on which are formed projections (5) that form a plurality of rows (6; 6a, 6b) extending from an equator (2) of the expandable socket (1). The projections (5) are arranged on the tongues (4) in such a manner that a row (6a) of projections (5) arranged in the center of the tongue (4) extends on a meridian (14) of the hemispherical socket (1) while at least one adjoining row (6b) of projections (5) extends in a line that extends at all points in parallel to the meridian (14) of the row (6a) of projections (5) arranged in the center and not through a pole (10) of the hemispherical expandable socket (1).