Abstract: An adapter for converting a tag-along or standard trailer to a gooseneck trailer. The adapter has a main elevated horizontal frame with three principal structures depending therefrom comprising: (1) a forward gooseneck of adjustable vertical length for connection to a gooseneck towing point on a tow vehicle; (2) an intermediate vertical-tension-resisting rectangular frame carrying a hitch ball to be received in a ball-hitch coupler of the standard trailer, and small light-weight retractable or removable wheels with pneumatic tires providing manual mobility of the adapter by a single person, with its weight balanced over the wheels, between the standard trailer and a parked adapter position when the adapter is disconnected from the trailer; and (3) a rear vertical-compression-resisting rectangular frame having a vertically adjustable horizontal beam member which spans, rests atop, and is secured to, upper surfaces of trailer tongue members extending rearwardly divergently from the trailer ball-hitch coupler.