It’s important to remember that Mary herself does not perform miracles; only God can do that. The Church does believe, however, that miracles can be related to the intercession and prayers of Mary on our behalf (see the story of the wedding at Cana in the Gospel of John), so over the years there have been many reported miracles connected with Marian shrines or apparition sites.
The spring in Lourdes, France, where Mary appeared to a young peasant girl named Bernadette Soubirous in 1858, is associated with many healings. Thousands have been reported over the years; of these, 68 have been recognized as miraculous by the Lourdes Medical Bureau, which investigates miracles according to a list of stringent criteria, a process which can take years.
One of these healings is described in Elizabeth Ficocelli’s book Lourdes: Font of Faith, Hope and Charity (Paulist Press, 2007). In 1962, a young Italian man named Vittorio Micheli was diagnosed with a malignant tumor in his pelvis, which had destroyed most of his left hip. The cancer had spread, and the doctors declared it to be terminal. Mr Micheli’s brother encouraged him to go to Lourdes, where he bathed in the spring. Upon his return home, his pain went away and his appetite returned. Within a few months, X-rays showed that his hip had been miraculously reconstructed. Mr. Micheli’s case was investigated and, in 1976, was officially declared to be the 63rd miracle of Lourdes.