Maryland Route 188 begins at MacArthur Boulevard in Glen Echo as a two-lane road with a speed limit of 25 mph (40 km/h). The road heads north and then east through a densely populated residential area with occasional schools, churches, and businesses. After passing Selkirk Drive, MD 188 temporarily widens to a four-lane divided highway for its intersection with Maryland Route 190 (River Road), which provides access to Washington and the Capital Beltway. After crossing MD 190, the road returns to its two-lane status, a configuration that continues to its eastern terminus.
MD 188 continues east through suburban residential areas. At Elmore Lane, a service road begins to parallel the eastbound direction. This service road continues past Whittier Boulevard to just beyond Marbury Road. Opposite Marbury Road is the entrance to the Landon School. After Marbury Road, the road curves to the right and then back to the left before the intersection with Maryland Route 191 (Bradley Boulevard). After crossing MD 191, MD 188 continues due east toward downtown Bethesda. The road's eastern terminus is at a five-way intersection with Maryland Route 187 (Old Georgetown Road), Arlington Road, and St. Elmo Avenue. Traffic coming from MD 188 may only access MD 187 south and Arlington Road. To access MD 187 north, traffic must turn left at Cordell Avenue, the previous street.