Known as Main Street, the state highway runs 1.73 miles (2.78 km) from SR 616 and SR 749 north to Interstate 81 (I-81) within Rural Retreat in western Wythe County.

SR 90's southern terminus is at the center of the town of Rural Retreat at the intersection of Main Street and Baumgardner Avenue.

The state highway heads north and has a grade crossing of Norfolk Southern Railway's Pulaski District.

SR 90 leaves the town limits and intersects US 11 (Lee Highway) at Staley Crossroads.

The state highway continues to its northern terminus at the southbound ramps of its diamond interchange with I-81.