Known as Newtowne Neck Road, the state highway runs 4.66 miles (7.50 km) from St. Francis Xavier Church near Compton north to MD 5 in Leonardtown.

MD 243 heads north through a mix of farmland and forest to the hamlet of Compton, where the highway intersects Bayside Road, which leads to the waterfront community of St. Clement Shores.

The state highway veers northeast and intersects Bull Road, which leads to the Society Hill neighborhood and Breton Bay Country Club.

[6][7] Finally, MD 243 was extended south to its present terminus at St. Francis Xavier Church in 1932.

[11] This portion of MD 943, a number later assigned to Warren Road in Cockeysville in Baltimore County, was removed from the state highway system in 1999.