TT 2010 was worth around £19 million pounds to the Isle of Man.
The figure has been calculated by the Economic Affairs Division of the Treasury, following what's described as the most rigorous study to date of visitor numbers to the Island for the races.
The main findings of the survey are that 31,000 people came to the Island for TT 2010, spending an average of £620.
Numbers peaked on Mad Sunday, when there were 21,500 visitors.
Seventy-two per cent of the 6,550 people questioned were repeat visitors, with 62 per cent saying they tended to visit the Island at least once every two years.
The interviews were carried out as the passengers left the Island, between the Monday of practice week and the Wednesday following senior race day.