Field work in the summer of 1990 on Martinique, French Antilles, led to the discovery of a new species of Colostethus (Anura: Dendrobatidae). The new species is a small (snout-vent length <20 mm), brown frog which can easily be identified by its distinct ventral coloration. The venter is a uniform pale orange in life, with males having a dark throat and a black collar covering the entire hyoid region. Toe webbing is reduced to barely perceptible vestigial webbing between toes III and IV. The species has a crepuscular activity cycle and a distinctive, high-pitched call. Its habitat is restricted to the upper slopes of Montagne Pelee on the island of Martinique in the central Lesser Antilles. Its discovery is remarkable because it was not recognized previously on this otherwise herpetologically well-known island, and because it is the only known member of the frog family Dendrobatidae endemic to an oceanic island.