The surname Postregna is of toponymic origin and derives from the name of the locality of Postregna, in the Natisone valley, north-east of Cividale del Friuli. On this point E. Rossoni and B. Zuanella agree, noting that the surname was formed to indicate the geographic origin of the line.

B. Zuanella further explains that originally the form "de Postregna" was used to designate those who came from that place, and that in time the preposition was lost, leaving the place name as the surname. In this way, the surname clearly reflects its territorial origin, in keeping with the usual processes of surname formation in Italy.