Abstract: A window assembly with a safety catch comprises a manually movable window sash which normally slides between a raised and a fully lowered position within a surrounding window frame. A weight is connected to the sash by a cable which counter-balances weight of the sash. The safety catch prevents downward falling of the sash to the fully lowered position in the event of breakage of the cable. The safety catch comprises a sash block spaced below the weight and clear of the sash when the cable is intact and the weight is positioned to fall if released from the sash to move the sash block to a blocking position which holds the sash above its fully lowered position.