A retaining wall block (1) has parallel top and bottom faces (2, 3), a front face (4), a rear face (5), first and second side wall faces (6, 7) and a vertical plane of symmetry (S) extending between the front and rear faces (4, 5). The block (1) is formed as a body portion (8) including the front face (4), a head portion (9) including the rear face (5) and a neck portion (10) connecting the body portion (8) and the head portion (9). The body, head and neck portions (8, 9, 10) each extend between the top and bottom faces (2, 3) and between the first and second side wall faces (6, 7). An opening (13)' extends through the neck portion (10) from the top face (2) to the bottom face (3), dividing the neck portion (10) into first and second neck wall members (14, 15) extending rearwardly from the body portion (8) to the head portion (9). First and second pin holes (16 and 17) are each disposed in the body portion (8) and open onto the top face (2) for receiving a pin (50, 51) with a free end of the pin protruding beyond the top face. First and second pin receiving cavities (18, 19) are each disposed in the body portion (8) and open onto the bottom face (3) for receiving the free end of a pin (50, 51) received in a pin hole (16 and 17) of an adjacent block (1) disposed therebeneath so as to interlock the blocks (1) with a predetermined setback. The neck wall members (14, 15), pin holes (16 and 17) and pin receiving cavities (18, 19) are positioned such that a first plane (P1) extending parallel to the plane of symmetry (5) passes through the first pin receiving cavity (18), first pin hole (16) and first neck wall member (14) and a second plane (P2) extending parallel to the plane of symmetry (5) passes through the second pin receiving cavity (19), second pin hole (17) and second neck wall member (15).