Stem-end rot, caused by Lasiodiplodia theobromae, is an important postharvest disease of pa- paya in Brazil. The use of fungicides is one of the main disease management measures. However, there are no data available on the sensitivity of L. theobromae to thiophanate methyl (methyl benzimidazole carbamate), the most common fungicide used in papaya orchards in northeastern Brazil. Thus, the effective concentration that results in 50 % of mycelial growth inhibition (EC50) of 109 isolates, representing five populations of the pathogen was estimated in vitro. Seven components of fitness were measured for the 10 isolates with lower and high values of EC50. Of the 109 isolates, 20.2 % were resistant to the fungicide with EC50 values greater than 300 μg ml−1, whereas the remaining 79.8 % were sensitive with an average EC50 of 1.87 μg ml−1. The EC50 values for the resistant isolates were significantly (P≤0.05) higher than those for the sensitive isolates. When the fitness components were evaluated, only in relation to the spore production was significant differ- ence among sensitive and resistant isolates, and resistant isolates showed sporulation capacity significantly lower than the S isolates, indicating a fitness cost.