The scholars consulted agree that this surname derives from the hypocoristic Naldo, an apocopated form obtained by aphaeresis from personal names ending in -naldo, such as Arnaldo, Monaldo, and above all Rinaldo or Rainaldo. It is also recorded as deriving directly from given names such as Arnaldo and Rinaldo. E. Rossoni specifies that these forms could have been transmitted directly or through diminutives, and that the original bearers of those names would have been the founders of the line.

Regarding geographical distribution, F. De Laurentiis and E. De Felice identify Tuscany and Emilia as the main areas of presence. Rossoni broadens this picture, indicating that the surname is spread across central and northern Italy, with a particular concentration in Emilia, Romagna, and Tuscany. The variant Naldini appears in the area of Forlì — specifically at Forlì and Meldola — in the area of Ravenna — at Ravenna and Faenza — and in Tuscany, in the areas of Florence, Siena, Arezzo, and Grosseto. The variant Naldo, by contrast, is very infrequent and is characteristic of Veneto, with a specific presence in the area of Belluno, in the localities of Sospirolo and Belluno.