Mango, which is an important tropical fruit crop in the region of Piura (Peru), is known to be prone to a range of diseases caused by Lasiodiplodia spp. The aim of this study was to evaluate the incidence and prevalence of mango dieback in the region of Piura, and to identify the species of Lasiodiplodia associated with the disease and evaluate their pathogenicity towards mango. Mango dieback was present in all orchards surveyed but incidence varied with location. Identification of fungal isolates was based on morphological and cultural characteristics as well as sequence data of the rDNA internal transcribed spacer region (ITS) and translation elongation factor 1-alpha gene (tef1-α). The following Lasiodiplodia species were identified: Lasiodiplodia brasiliense, Lasiodiplodia egyptiacae (for which the new combination Lasiodiplodia laeliocattleyae is introduced), Lasiodiplodia iraniensis, Lasiodiplodia pseudotheobromae, Lasiodiplodia theobromae, and a Lasiodiplodia sp. Individual and combined gene genealogies suggest that this Lasiodiplodia sp. is possibly a hybrid of Lasiodiplodia citricola and Lasiodiplodia parva. Apart from Lasiodiplodia theobromae, which was the most prevalent species, all other species are newly reported from Peru. Moreover, L. iraniensis is reported for the first time on mango. Inoculation trials of mango plants confirmed Koch's postulates, and revealed differences in aggressiveness among species and isolates.