Maryland Route 187 (MD 187) is a state highway in the U.S. state of Maryland. Known as Old Georgetown Road, the state highway runs 5.32 miles (8.56 km) from MD 355 and MD 410 in Bethesda north to MD 355 in North Bethesda. MD 187 runs parallel to MD 355 through suburban areas of southern Montgomery County.

MD 187 begins at an intersection with MD 355 (Wisconsin Avenue) and westbound MD 410 (East–West Highway) next to the Bethesda station of the Washington Metro in downtown Bethesda. The state highway heads northwest as a two-lane one-way street to Woodmont Avenue. Southbound MD 187 traffic is required to turn north or south onto Woodmont Avenue. Woodmont Avenue, which becomes a southbound one-way street at the intersection, leads to Montgomery Lane, which provides access to MD 355 and eastbound MD 410 (Montgomery Avenue). MD 187 heads northwest from Woodmont Avenue as a five-lane highway with center turn lane that passes through a five-way intersection with MD 188 (Wilson Lane), Arlington Road, and St. Elmo Avenue and leaves downtown Bethesda. The state highway veers north and becomes a six-lane divided highway at Suburban Hospital, which sits opposite the southern end of the NIH campus. MD 187 intersects several entrances to the federal campus and passes to the east of the tiny village of Oakmont.

MD 187 enters North Bethesda at its diamond interchange with Interstate 495 (Capital Beltway) (I-495). The state highway intersects Democracy Boulevard, a county highway that heads west past Walter Johnson High School and the Montgomery Mall, and meets I-270 (Eisenhower Memorial Highway) at a diamond interchange whose ramps also connect with Rockledge Boulevard. MD 187 heads northeast to its intersection with Executive Boulevard, where the state highway curves to the east and reaches its northern terminus at MD 355 (Rockville Pike) just north of the White Flint Metro station.

The entire route is in Montgomery County.

MD 187B is the designation for the 0.08-mile (0.13 km) section of Rockledge Boulevard within MD 187's interchange with I-270 in North Bethesda.