The cap of Gomphidius smithii is about 1.5-7 centimeters in diameter. It starts out rounded, before becoming convex and eventually flat. The surface of the cap is slimy. The stipe is about 4-7 centimeters long and 0.5-1 centimeters wide, with a veil. Unlike many other Gomphidius species, G. smithii is not yellow at the base of the stipe. The gills are decurrent and start out white, before graying with age. The spore print is dark gray, sometimes almost black.