Hi Judy, Not all called by the name "O'Brien" descend from the one, true, Ó Brian sloinne. For example, some of the Ó Broin ('Byrne') sloinne of Cos. Wicklow and Kildare are now called "O'Brien," as are some of the Mac Braoin ('Breen') sloinne of Cos. Fermanagh and Cavan, and some of the Bryans of Cos. Kilkenny and Wexford. But you're from Munster, from Limerick, from Brian's own stomping ground. There's no doubt your family descends directly from Brian Bóramha unless there was an adoption somewhere along the way. Le gach dea-ghuí / Best, Jerry