Myotis simus is apparently restricted to tropical and subtropical South American lowlands, with a possible disjunction isolating northern and southern populations. Twenty-eight museum and literature records were assembled and analysed in the context of a taxonomic review of South American species of Myotis. In order to model the distribution of M. simus, to reveal putative areas of occurrence and environmental constraints to its distribution, as well as to test the previously proposed hypothesis of disjunct distribution, Maximum Entropy Algorithm (MaxEnt) was implemented on the information retrieved from the sampling localities, using 9 environmental variables. Two regions with increased probability values were revealed in the Amazon and Paraná basins, connected by a bottleneck in southeastern Bolivia, which provides further support for the previously proposed hypothesis of disjunctive distribution. The predicted distribution for M. simus was strongly associated with the drainage basins, precipitations of the driest quarter, mean temperatures of the warmest quarter and altitude. The Andean eastern slopes and the Guyana, Paraná and Central Brazilian plateaus delimit the geographical distribution of M. simus, and the confirmed records document its presence in both terra firme and floodplain areas in lowland forest and savanna formations across South America.