An apparatus for removably attaching a lateral support to a chair, the apparatus comprising: a lateral support (30, 130) for supporting a person seated in the chair to sit upright, a support frame (1, 101) removably attachable to the chair to attach the lateral support (30, 130) to the chair, the support frame (1, 101) comprising two side members (2, 102) and a lateral member (4, 5, 105) coupled between the side members (2, 102) spacing the side members (2, 102) apart by a lateral distance, and an adjustment mechanism (6, 7, 106) to adjust the lateral distance between the two side members (2, 102) to releasably clamp the chair between the side members (2, 102), wherein the support frame (1, 101) is configured to be fitted to the chair by clamping the support frame (1, 101) to the seat back of the chair, in use said seat back being clamped between the two side members (2, 102) with the lateral member (4, 5, 105) extending laterally across the seat back behind the chair, characterized in that the apparatus further comprises: an attachment arm (15, 115) attached to a said side member (2, 102), the attachment arm (15, 115) and the corresponding side member being adapted for positional adjustment there between, the lateral support (30, 130) being attached to the side member by the attachment arm (15, 115), and a connecting element (132a, 132b) for supporting the lateral support (30, 130) from the attachment arm (15, 115), the connecting element (132a, 132b) comprising a length adjustable assembly for adjusting the length of the connecting element (132a, 132b) for positioning the lateral support (30, 130) laterally. a lateral support (30, 130) for supporting a person seated in the chair to sit upright, a support frame (1, 101) removably attachable to the chair to attach the lateral support (30, 130) to the chair, the support frame (1, 101) comprising two side members (2, 102) and a lateral member (4, 5, 105) coupled between the side members (2, 102) spacing the side members (2, 102) apart by a lateral distance, and an adjustment mechanism (6, 7, 106) to adjust the lateral distance between the two side members (2, 102) to releasably clamp the chair between the side members (2, 102), wherein the support frame (1, 101) is configured to be fitted to the chair by clamping the support frame (1, 101) to the seat back of the chair, in use said seat back being clamped between the two side members (2, 102) with the lateral member (4, 5, 105) extending laterally across the seat back behind the chair, characterized in that the apparatus further comprises: an attachment arm (15, 115) attached to a said side member (2, 102), the attachment arm (15, 115) and the corresponding side member being adapted for positional adjustment there between, the lateral support (30, 130) being attached to the side member by the attachment arm (15, 115), and a connecting element (132a, 132b) for supporting the lateral support (30, 130) from the attachment arm (15, 115), the connecting element (132a, 132b) comprising a length adjustable assembly for adjusting the length of the connecting element (132a, 132b) for positioning the lateral support (30, 130) laterally. an attachment arm (15, 115) attached to a said side member (2, 102), the attachment arm (15, 115) and the corresponding side member being adapted for positional adjustment there between, the lateral support (30, 130) being attached to the side member by the attachment arm (15, 115), and a connecting element (132a, 132b) for supporting the lateral support (30, 130) from the attachment arm (15, 115), the connecting element (132a, 132b) comprising a length adjustable assembly for adjusting the length of the connecting element (132a, 132b) for positioning the lateral support (30, 130) laterally.