PR 100 begins at the Queen Isabella Causeway in Port Isabel, and continues west as State Highway 100.

A 2.37-mile bridge crosses Laguna Madre, the only road connecting South Padre Island to the mainland.

It then enters the town of South Padre Island and intersects itself near the Schlitterbahn water park and resort.

The section of the road south of this intersection acts as a spur for the southernmost part of the island.

It ends shortly after entering the Padre Island National Seashore.