Known as Aris T. Allen Boulevard, the state highway runs 2.68 miles (4.31 km) from U.S. Route 50 (US 50)/US 301 in Parole east to Bywater Road and Forest Drive in Annapolis.

MD 665 heads southeast as a four-lane freeway through a single-point urban interchange with Riva Road.

The highway turns east and meets MD 2 (Solomons Island Road) at a partial cloverleaf interchange.

The roadway continues southeast as Forest Drive, a four-lane road with a center turn lane.

Forest Drive intersects MD 387 (Spa Road) and Bay Ridge Avenue on its course along the southern fringe of the city of Annapolis.

In October 1992, state officials named MD 665 for Aris T. Allen, a doctor and former member of the Maryland General Assembly who had died in 1991.

When MD 665 was being planned in the early 1980s, Allen was instrumental in rerouting the highway to bypass an African-American neighborhood instead of slicing through and displacing its residents.