The breeding season of White-throated Mountain-gem extends from October through April (Hartman 1957, Stiles and Skutch 1989). At Boquete, Panama, one nest with two nestlings was found on 16 February 1956 (Hartman 1957). The nest is placed in a bush in the understory, at the edge of a forest or open field, from about 1 to 3 meters above the ground (Stiles and Skutch 1989). The nest is a rounded cup, with the inner part composed of fine brown plant fibers and the outside decorated almost completely with green moss and with few lichens on the upper parts (Hartman 1957, Stiles and Skutch 1989). The outer dimensions of one nest were 59 x 59 mm; and the dimensions of the inside of the cup were 27 mm in diameter and 20 mm in depth (Hartman 1957). There is no published information regarding clutch size, the color or dimensions of the eggs, or on incubation, nestling growth rates, or parental care.