Five girls aged just 13 were treated at the Rotunda's Sexual Assault Treatment Unit in 2012.
The Dublin hospital's annual report shows that 318 men and woman presented for help at the facility and three quarters of those had taken alcohol.
The statistics also show that two thirds knew their attacker but one in five chose not to report the assault to the Gardaí.
Medical Director at the Sex Assault Unit Maeve Eogan said the age range of those presenting was quite broad.
"We saw people ranging from the age of 13 to the age of 78…In 2012, we saw five girls less than 14 years," she said.
"Even though our services are primarily for those over 14 years, it can sometimes be hard for paediatric services to be accessed (so) we look after those children here as well."
The Sexual Assault Treatment Unit (SATU) was established in 1985, and was the first dedicated unit of its kind in Europe.