We describe a new species of Allobates from the Magdalena Valley in Colombia. The new species and its sister species, A. talamancae, are the only two species of Allobates known to occur west of the Andes. The new species differs from A. talamancae in being smaller, possessing a diffuse pale oblique lateral stripe, and exhibiting strong swelling of finger III in adult males. Tadpoles also differ in the relative size of anterior and posterior labial papillae; in the new species anterior papillae are conspicuously larger than posterior papillae, whereas in A. talamancae they are subequal in size. Allobates talamancae and the new species are allopatric. Among the cis-Andean species of Allobates, the new species most resembles A. melanolaemus, which also possesses a diffuse pale oblique lateral stripe and a solid black throat in adult males, but from which it differs in being smaller and adult males having finger III strongly swollen and solid black pigmentation covering the chest and most of the belly.