Lactarius vietus (commonly known as the grey milkcap) is a species of fungus in the family Russulaceae, first described by Elias Magnus Fries. It produces moderately sized and brittle mushrooms, which grow on the forest floor or on rotting wood. The flattened-convex cap can vary in shape, sometimes forming the shape of a wide funnel. It is typically grey, but the colour varies. The species has crowded, light-coloured gills, which produce white milk. The spore print is typically whitish, but also varies considerably. The mushrooms typically have a strong, acrid taste and have been described as inedible, but other authors have described them as consumable after boiling. L. vietus feeds by forming an ectomycorrhizal relationship with surrounding trees, and it favours birch. It grows in autumn months and is fairly common in Europe, North America and eastern Asia.