MD 117 begins at an intersection with MD 28 (Darnestown Road) between Dawsonville and
Beallsville. The highway heads north as two-lane undivided Bucklodge Road past the historic home
Friends Advice, then curves northeast and crosses Bucklodge Branch. MD 117 passes under
CSX's
Metropolitan Subdivision railroad line, which carries MARC's Brunswick Line. The highway curves southeast at its tangent junction with Barnesville Road and assumes that name as it approaches the village of Boyds. At the southern end of
MD 121 (Clarksburg Road), MD 117 turns south onto Clarksburg Road and passes under the railroad again adjacent to the
Boyds station serving MARC. Just south of the railroad, the highway turns east onto Clopper Road, which parallels the railroad then veers away southeast and crosses
Little Seneca Creek. East of Little Seneca Creek, MD 117 enters the suburban area of Germantown. The highway expands to a four-lane divided highway south of
Kingsview Middle School and intersects
MD 118 (Germantown Road), the main street through Germantown that serves the
Germantown MARC station. MD 117 gains a third eastbound lane to
MD 119 (Great Seneca Highway), where the divided highway ends and soon drops to two lanes as it leaves Germantown. The highway crosses
Great Seneca Creek and passes an entrance to Seneca Creek State Park. MD 117 expands to a four-lane undivided highway as it enters the city of Gaithersburg. The highway intersects Metropolitan Grove Road, which leads to the
eponymous MARC station. MD 117 expands to a six-lane divided highway west of its intersection with MD 124 (Quince Orchard Road). The highway continues east as West Diamond Avenue along the northern edge of an
unincorporated enclave within the city of Gaithersburg. The enclave contains the campus of the
National Institute of Standards and Technology, whose main entrance is along MD 117 east of MD 124. East of the federal agency's campus, MD 117 has a partial interchange with I-270 (Eisenhower Memorial Highway). The interchange consists of a straight ramp from the state highway to southbound I-270 and a loop ramp from northbound I-270 to MD 117. Connections with I-270 in the direction of
Frederick are made via the freeway's interchange with MD 124 to the north. A
park and ride lot is located within the loop ramp from northbound I-270. MD 117 drops to three lanes through the interchange, then expands to a four-lane divided highway again at Perry Parkway. The highway passes south of
The Avalon School before it fully re-enters the city of Gaithersburg at its junction with Muddy Branch Road, east of which the highway drops to two lanes and reaches its eastern terminus at
MD 117A, an
unsigned connector between MD 117 and southbound MD 355 (Frederick Avenue). West Diamond Avenue continues east as a city street that parallels the Metropolitan Subdivision rail line under MD 355. West Diamond Avenue becomes Old Towne Avenue, which intersects Fulks Corner Road—which provides access to northbound MD 355—on its way to downtown Gaithersburg and the
Gaithersburg MARC station. MD 117 is a part of the
National Highway System as a principal arterial between MD 118 and MD 119 in Germantown. ==Cultural significance==