May 5 - At its headquarters in Kingsbridge, CIÉ signs a £4.75 million contract to replace its steam trains with diesel locomotives.
May 16 - 30,000 march through Dublin city in a huge Marian Year procession. It is the city's greatest display of Catholic faith since the International Eucharistic Congress since 1932.
May 18 - Fianna Fáil lose four seats in the general election. The second inter-party government under John A. Costello comes to power.