Infection of malformed and nonmalformed mango (Mangifera indica) trees byFusarium subglutinanswas assessed in Florida. All malformed floral panicles, but only 50% of the nonmalformed panicles, were infected by the fungus. When within-panicle infection was evaluated, an average of 84.5 % of the small pedicel and peduncle tissue pieces from malformed panicles were infected. When malformed and nonmalformed panicles were both assessed, 68.3% of the tissues from malformed panicles, but only 11.7% from nonmalformed panicles, were infected. Slight infection (2.2%) was observed in branch tissue that supported malformed panicles, and the fungus was never isolated from branches that supported nonmalformed panicles. In nutritional complementation tests with nitrate nonutilizing (nit) mutants, 55 of 64 isolates ofF.subglutinansfrom malformed mango panicles were in the same vegetative compatibility group. The data indicate that mango malformation in the study area was significantly correlated (P < 0.0001) with infection by genetically related populations ofF.subglutinans. The far greater prevalence ofF.subglutinansin malformed than in asymptomatic panicles suggests that malformation symptoms develop in floral tissues only after they are extensively colonized by this fungus.Key words:Fusarium subglutinans, mango malformation, vegetative compatibility.