Although it has been a common belief that he was from FUJIWARA no Uona line of the Northern House of the Fujiwara clan, there is a view that "in fact, he was from the Tottori clan from Fumiogori in Shimotsuke Province and Hidesato himself used the family name, Fujiwara, deceptively" (Another view says that "Tottori" was the name of his parents' family which had been serving as Zaichokanjin (the local officials in Heian and Kamakura periods) from ancient times.
出自を藤原北家魚名流とするのが通説だが、｢実際には下野国史生郷の土豪・鳥取氏で、秀郷自身が藤原姓を仮冒した｣という説もある（あるいは古代から在庁官人を務めた秀郷の母方の姓とする）。