In the Atusparia sector, Tocache, of the San Martin region in Peru, two-year-old plants of Theobroma cacao L. (Malvaceae) of the CCN-51 clone showed for the first time in January 2010, symptoms of leaf yellowing, wilt and dieback, with an internal obstruction of the vascular system of the plant. To isolate the fungus, diseased tissues were cultured in Petri dishes containing potato dextrose agar oxytetracycline, and the identification was based on morphological and microscopic analyses and by the Sanger sequencing. Pathogenicity tests were carried out on three-months-old T. cacao ICS-1 clone plants and were inoculated with a conidia suspension of 1x107 cfu/mL employing two inoculation methods (Drench to the soil and stem puncture). Likewise, the antagonistic capacity (mycoparasitism and antibiosis) was established in vitro with endophytic Trichoderma isolates on the pathogen. With both inoculation methods symptoms of wilt of different degrees of severity were observed and the causal agent of sudden death in T. cacao was confirmed to be the fungus Verticillium dahliae Kleb. blast sequence analysis revealed that the isolate showed 100 % homology with V. dahliae sequences in GenBank. Trichoderma TE-91 was identified as the most aggressive mycoparasite because its metabolites inhibited completely the mycelial growth of the pathogen.