Pathogenicity of Musicillium theobromae (Turconi) Zare & W. Gams (syn. Stachylidium theobromae Turconi, Verticillium theo- bromae E.W. Mason & S. Hughes) causing Banana cigar end rot disease has fulfilled Koch’ s Postulates for the first time . To assess and prove the pathogenicity, M. theobromae mycelial discs and conidia were inoculated in triplicate to surface-disinfested green banana fruits. The bananas were infected both through artificial wounds as well as through intact unwounded fruits. After inoculation, the bananas were covered with moist cotton and incubated for 30 days at 23°C. Plain moist cotton was used on the controls. Those inocu- lated treatments kept under high relative humidity exhibited symptoms of banana cigar end rot disease. The controls and those kept under low relative humidity did not develop symptoms and remained healthy. The results indicated that both optimum temperature and high relative humidity are necessary for infection onset and disease development. It was also determined that infection can occur both through wounds and intact unwounded fruit epidermis. The cultural characteristics in M. theobromae were also investigated. It was found that the best mycelial growth occurred on potato dextrose agar (PDA) and the optimum pH for mycelial growth was 8.