Citron (Citrus medica L.) stems and branches showing numerous round to elongated knots were brought to the laboratory for diagnosis. Microscopic studies of dried small knots revealed the presence of picnidia bearing conidia typical of the fungus Sphaeropsis tumefaciens Hedges. Original disease symptoms were reproduced through pathogenicity trials conducted in the greenhouse.En troncos y ramas del cidro (Citrus medica L.) aparecieron numerosos nudos entre redondos y alargados. Pedazos secos de dichos nudos vistas al microscopio revelaron la presencia de picnidios con conidios típicos del hongo Sphaeropsis tumefaciens Hedges. En ensayos patogénicos realizados en invernaderos se reprodujeron síntomas iguales a la afección original.