Mother of twins and Aussie royal Princess Mary of Denmark will do a double act as the international patron of the Australian and Danish twin registries.

Princess Mary's patronage of the Australian Twin Registry, based at the University of Melbourne, and the Danish Twin Registry was announced in a ceremony in Denmark at 11pm (AEDT) on Tuesday.

Australian Twin Registry director John Hopper said as a mother of twins Princess Mary was a fantastic ambassador for twin research.

"We are extremely thrilled about the announcement and hope the crown princess's patronage will raise awareness of the importance of twin research on a range of health issues from cancer, to diabetes, epilepsy, heart disease, to osteoporosis and Alzheimer's disease," the Melbourne University professor said in a statement on Tuesday.

Crown Princess Mary was born Mary Donaldson in Hobart and married Crown Prince Frederik in 2004 in Copenhagen.

She is the mother of Prince Christian, Princess Isabella and two-year-old twins Prince Vincent and Princess Josephine.

The Australian Twin Registry supports medical studies involving twins, enabling researchers to study the impact of genetic and environmental factors on health.