It is notable as the northernmost point of Wales.
Middle Mouse is a popular diving location, being host to species such as anemones and sea squirts. Local legend has it that St Patrick was shipwrecked there, giving rise to its alternative name.
He then swam ashore and eventually founded the nearby church of Llanbadrig in about 440 AD, believed to be the oldest Christian site in Wales.
Whether or not this is the case, the S.S. Liverpool was certainly shipwrecked near Middle Mouse.
In 2005, the island was put up for sale.