The production of avocado in Peru has been increasing over the last five years and it represents a major export commodity. However, dieback symptoms, typical of Botryosphaeriaceae, have been observed in avocado orchards throughout the country, leading to economic losses. Thus, this study aimed to evaluate the diversity and pathogenicity of species associated with dieback of avocado trees, in the Peru’s Pacific coastline. On the basis of morphological and cultural characters, as well as phylogenetic analysis of the internal transcribed spacer region (ITS) and part of the translation elongation factor 1-α gene (tef1-α), the isolates were identified as belonging to three Lasiodiplodia species, namely L. theobromae, L. laeliocattleyae and L. pseudotheobromae. Inoculation in cv. ‘Hass’ plants confirmed the pathogenicity of Lasiodiplodia species and revealed differences in aggressiveness among species and isolates. Lasiodiplodia laeliocattleyae is reported for the first time in avocado trees associated with dieback symptoms, which together with L. theobromae and L. pseudotheobromae may represent a threat to Peruvian avocado plantations.