The valve pin adjustment system is provided for use in valve gated injection molding applications which enables adjustments to the positioning of the valve pin without necessitating removal of the clamping plates and valve assembly components, including valve pins. A piston associated with the valve pin includes a cylindrical body having first and second co-axially aligned internally threaded bores of respective first and second diameters. Preferably, the threads formed in the first and second bores are of the opposite hand. First and second externally-threaded cylindrical valve pin positioning members are respectively received in the first and second bores. Each of the positioning members includes a head portion and a tip portion. The tip of the second positioning member is in contact with the head of the first positioning member to lock the first positioning member in place, and the tip of the first positioning member is in contact with a head portion on the valve pin to locate the valve pin.