Limia islai, a new species of livebearing fish, is described from Lake Miragoane in south-western Haiti on Hispaniola. The new species has a conspicuous barred pattern consisting of several (4-12) black bars along the body, ray 4p serrae of the gonopodium in males with 10 segments and origin of dorsal fin in females slightly behind the origin of the anal fin. Although the new species colour pattern is similar to that of the humpbacked limia Limia nigrofasciata Regan 1913, L. islai sp. nov. has exclusive morphological features, such as slender body, lack of hump anterior to dorsal fin in males and presence of specific features in the gonopodial suspensory, which allow an unambiguous diagnosis from L. nigrofasciata. L. islai further differs from L. nigrofasciata in reproductive behaviour since L. islai males rely on sneak copulations and gonopodial thrusting, whereas L. nigrofasciata display an elaborate courtship behaviour. The new species is also genetically distinct in both nuclear (Rh, Myh6) and mitochondrial (12S, ND2, D-loop, Cytb) genes from other species in the genus showing reciprocal monophyly. The description of this new Limia species from Lake Miragoane confirms this lake as an important centre of endemism for the genus, with a total of eight endemic species described so far.