Brachypelma smithi is a species of spider in the family Theraphosidae (tarantulas) native to Mexico. It has been confused with Brachypelma hamorii; both have been called Mexican redknee tarantulas. Mexican redknee tarantulas are a popular choice as pets among tarantula keepers. Many earlier sources referring to B. smithi either relate to B. hamorii or do not distinguish between the two species. B. smithi is a terrestrial tarantula native to Pacific coast of the Mexican state of Guerrero.
Brachypelma smithi is a large spider. A sample of seven females had a total body length (excluding chelicerae and spinnerets) in the range 52–59 mm (2.0–2.3 in). A sample of eight males were slightly smaller, with a total body length in the range 44–49 mm (1.7–1.9 in). Although males have slightly shorter bodies, they have longer legs. The fourth leg is the longest, measuring 70 mm (2.8 in) in the type male and 66 mm (2.6 in) in a female. The legs and palps are bluish black with three distinctly colored rings: dark reddish orange on the part of the patellae closest to the body with light yellowish pink further away, pale yellowish pink on the lower part of the tibiae, and pinkish white at the end of the metatarsi. Adult males have a yellowish brown carapace; the upper surface of the abdomen is black. Adult females vary more in carapace color and pattern. The carapace may be mainly bluish black with a light brown border, or the dark area may be broken up into a “starburst” pattern or almost reduced to two dark patches in the eye area.