Arctostaphylos insularis is a large, spreading shrub reaching over 2 metres (6 ft 7 in) tall and known to exceed 5 metres (16 ft 5 in) in width. It has waxy, reddish bark and the smaller twigs sometimes have bristly glandular hairs. The leaves are shiny green and smooth, generally oval in shape and slightly convex, and up to about 4.5 centimetres (1 3⁄4 in) long. The shrub blooms in many dense clustered inflorescences of urn-shaped flowers. The fruit is an orange-brown drupe up to 1.5 centimetres (5⁄8 in) wide.