In a night of mixed fortunes for the Welsh nationalist party, they made a historic gain in a seat famously won for them in 1966 by Gwynfor Evans, Plaid's first MP.
But they lost Ynys Mon, the constituency on the north Wales island of Anglesey - a seat previously held by party leader Ieuan Wyn Jones for fourteen years.
Plaid held onto its three other seats in the previous parliament - Caernarfon, Meirionedd Nant Conwy, and Ceredigion.
But despite securing sizeable swings the party failed, as it had hoped, to gain any foothold in the south Wales Valleys, where only two years ago it won prized seats in the fledgling Welsh Assembly.
Plaid's new MP for Carmarthen East and Dinefwr, Adam Price, welcomed his win over Dr Alan Williams as a "historic victory".
"We won because of a tangible shift towards us in the communties of the industrial valleys of Gwendraeth and the Amman," he said.
"I think we are in a very strong position to form a majority in the 2003 Assembly elections, " he said.
Plaid's leader Ieuan Wyn Jones stood down as an MP to concentrate on his role as assembly member .
He said he was very pleased that Adam Price had won in Carmarthen East from Labour and said it was a sign of the work he had put in to win the seat.
Mr Jones said it was a personal blow for him that the party had lost Ynys Mon, blaming the low turnout for the defeat.
He denied that Plaid had concentrated much of its resources on fighting the nearby seat of Conwy or that it was anything to do with the internal wrangling over the choice of a candidate.