The latching gas ON/OFF assembly (10) includes a housing with a female threaded bore (20) for receiving a male threaded neck of a gas tank cylinder (14) having a tank valve with a pin (24). A bonnet (18) is slidably connected to the housing (16) and slides between a forward OFF position and rearward ON position. A pin depressor (22) connected to the bonnet (18) with a transverse latch button (28) for locking the bonnet (18) in the ON position and for releasing the bonnet (18) from the ON position. When the bonnet (18) is slid to the rearward ON position it causes the pin depressor (22) to contact the pin (24) of the tank valve to permit gas to flow therefrom. The latching button (28) is spring-biased toward a locked position where a plate (28d) on the free end thereof removably resides in a complementary seat (44) in the housing (16).