Resumen: In a recent paper C. Miguel proved that the diameter of the commuting graph of the matrix ring Mn(R) is equal to 4 if either n = 3 or n = 5. But the case n = 4 remained open, since the diameter could be 4 or 5. In this work we close the problem showing that also in this case the diameter is 4. Idioma: Inglés Año: 2017 Publicado en: Bulletin of the Iranian Mathematical Society 43, 1 (2017), 217-221 ISSN: 1018-6301 Originalmente disponible en: Texto completo de la revista