[5] PR 391 begins at the at-grade interchange with Burntwood Road as a divided continuation of Highway 6 in the city of Thompson.

Known as Mystery Lake Road, PR 391 becomes the major arterial through Thompson, passing the Burntwood Regional Health Authority Hospital.

The route runs northwest and west for various points until reaching the area of Mooswuchi Lake.

There the route bends southwest and starts winding west until reaching a junction with a local road that connects to Nelson House.

The route turns northward at the Suwanee River, passing Turnbull Lake before reaching the town of Leaf Rapids.

After Leaf Rapids, the route runs northward for several kilometres, making the next bend to the northwest at Scotland Lake.

Passing north of the local railway junction, the route turns southwest and enters downtown Lynn Lake.

[2] By 1969, the section of modern-day PR 391 from Lynn Lake to the shores of the Churchill River near Leaf Rapids was constructed as an all-weather road.

[9] By 1973, PR 391 was extended westward to a creek from Footprint Lake with a span to Nelson House.

It is entirely a paved two-lane highway, now coming to dead end where it formerly serviced a now decommissioned mine.