Child safety seat

A child safety seat comprising a seat body (10) and a base (30) having the seat body (10) mounted thereon. The base (30) includes a bottom surface (32) adapted to rest on a vehicle seat, an abutment member (38) adapted to abut against the vehicle seat back, and a respective lateral belt guide (47, 48) on each side of the base (30) located above said bottom surface (32) and in front of said abutment member (38). At least one of the lateral belt guides comprises an open-ended slot (47) in the side of the base (30) and means (60) for varying the depth of the slot (47).