The Cairn Terrier has a fox-like expression. This peppy, very hardy little terrier has an abundant shaggy outer coat with a soft downy undercoat. The coat comes in red, brindle, blackish, sand and various shades of gray. Any color except white is acceptable, though dark points (ears, eyes and muzzle) are preferred. Adult coat color is hard to predict from the puppy coat as the color often continues to change for several years.

The Cairn Terrier has a compact body, about 14 inches from the forechest to back of the hindquarters. It is short with good bone structure. The head is broad with bushy topknot and eyebrows and black nose. It has a powerful but not heavy muzzle, a scissors bite and a wide, robust skull. The dark hazel eyes are deep set. The ears are small, pointy and erect. The short hairy tail is carried gaily. Faults to avoid are missing teeth, pinkish nose, white on the chest or feet and soft or curly body coat