He subsequently joined Barnsley. Having arrived at Barnsley on a short term deal, Letheren then signed a new deal to keep him at Oakwell until 2008 Two years after joining the club, he made his debut in the 3rd round of the FA Cup against Blackpool on 5 January 2008, as a half-time substitute, replacing the injured Heinz Müller. At 1–0 down 'the Tykes' went on to win the game 2–1, giving Letheren his first clean sheet on his debut. Barnsley that year went on to beat Liverpool & Chelsea and reached the FA Cup semi-finals.