The Little Dead Diamond River is a 7.1 mi river in northern New Hampshire in the United States. It is a tributary of the Dead Diamond River, located in the Androscoggin River watershed of Maine and New Hampshire. The Little Dead Diamond River rises in the town of Clarksville near the north end of Crystal Mountain, a 7 mi ridge with elevations ranging from 2400 to 3300 ft above sea level. 3081 ft Mount Pisgah lies just to the north of the headwaters. The river flows east into the Atkinson and Gilmanton Academy Grant, where it is joined by its west branch. The river then enters the Dartmouth College Grant and is joined by its south branch. The Little Dead Diamond then turns north, reenters the Atkinson and Gilmanton Grant, and joins the Dead Diamond River near the rapids and old logging camp known as Hell Gate.