The number and identity of the species of black widow spiders of the genus Latrodectus that inhabit Chile remain unclear. Here we present results of taxonomic work based on morphologic and molecular characters of a large series of specimens collected throughout Chile, which aimed to assess Chilean Latrodectus diversity. Results show that all studied populations belong to a single species, for which the correct name is Latrodectus thoracicus Nicolet 1849. Therefore, we remove this taxon from the synonymy of L. mactans (Fabricius, 1775). In addition, we suggest that L. mirabilis (Holmberg, 1876) may be junior synonym of L. thoracicus. We recognize two species of black widows for continental Chile, L. thoracicus andi. variegatus Nicolet, 1849. We provided an emended diagnosis and comprehensive description of L. thoracicus as well as new locality records and novel data on its natural history. Given our results, we recommend the continued collecting specimens and more collection based taxonomic work as the only way of gathering a correct appreciation of Latrodectus diversity in southern South America.