[1] He proved a capable commander and was able to defeat attempts by Oda Nobunaga to avenge his father-in-law Dôsan's death, but died of his illness in 1561.

However, rumors that Yoshitatsu was in fact not Dōsan's real son (that is, that he was actually the son of Toki Yorinari (Toki Yoshiyori), the shugo of Mino Province who Dōsan displaced in influence) persisted--with Dōsan apparently considering naming one of his other sons, Nagatatsu, as heir.

Though he actually did suffer from leprosy, Yoshitatsu feigned illness and murdered his two younger brothers in 1555, declaring war on Dōsan.

Yoshitatsu's vanguard opened the attack by crossing the river and cutting deeply into Dosan's ranks.

Yoshitatsu's son, Saitō Tatsuoki, was defeated by Oda Nobunaga in 1567 at the Siege of Inabayama; and the clan disappeared.