Mount Leinster (Irish: Stua Laighean) is the highest mountain in both County Carlow and County Wexford, Ireland. It is the highest of the Blackstairs Mountains at 796 metres (2,605 ft). A tall RTÉ television transmitter tops the peak with a mast height of 122 m.
The TV transmitter site is a popular location for hang-gliding enthusiasts to launch from. In 2003, a hang-glider pilot died from injuries sustained in the crash landing of his flight launched from the mountain. There is a memorial at the peak of the mountain.
The mountain is most often climbed from the Nine Stones, a landmark point at the foot of Mount Leinster, about 8 miles east of Borris. From Borris there is a road to a visitor car park on the mountain. From there the steep RTÉ access road leads to the summit. This road is closed to normal traffic and RTÉ have now fenced off the transmitter tower from public access to prevent vandalism.