Figures obtained by RTÉ's Morning Ireland indicate the scale of the staffing crisis among nurses.
It comes a day after a senior Government minister warned a further 1,000 nurses are scheduled to retire by the summer.
Almost 11,000 nurses left the profession between 2010 and 2013, including almost 4,000 who resigned their posts.
Yesterday, Minister for Primary Care Kathleen Lynch asked nurses who have emigrated to consider returning.
Union representatives say nurses have been leaving the profession in their thousands since the imposition of the Health Service Executive recruitment embargo in 2009.
They say the concerns raised yesterday by Ms Lynch are a delayed reaction to an ongoing issue.
HSE figures show 3,612 nurses retired between 2010 and 2013 and 308 left as a result of a permanent infirmity.
Minister Lynch said she hoped those mulling retirement this year would consider staying on while the HSE said it would prioritise the filling of vacant posts in areas where there is a shortage of staff.
Minister for Public Expenditure and Reform Brendan Howlin has said there were real issues in relation to a number of skill sets where Ireland was competing directly with the health services of Britain, Canada and the UIS.
He said there was an overall package that Ireland could not provide for every employee in a health service of its scale, saying the Government had to look at the issue in a package way.
Minister Howlin also said the HSE was processing nearly 4,000 applications from qualified nurses.
