Japan's Crown Princess Masako is suffering from Adjustment Disorder, a mental condition brought on by stress, the Imperial Household Agency has said.
Crown Princess Masako (R) is under pressure to have a boy
It was the first time the princess, who has not been seen in public since 2003, has been linked to a specific illness.
Her husband, Prince Naruhito, heir to the Japanese throne, has said she is exhausted by pressures of royal life.
The Princess, a former diplomat, is thought to feel especially pressured to produce a male heir.
The Imperial Household Agency said in a statement that the princess' stress was "caused by her special status as a crown princess, problems relating to her pregnancy and miscarriage, and her busy life, in which she has difficulties drawing a line between the public and the private".
Media pressure was blamed for a miscarriage in 1999. She then gave birth to a girl, Aiko, but only boys can succeed to the Japanese throne.
Only males can ascend the Japanese throne
If Prince Naruhito died without a male heir, his brother, Prince Akishino, succeeds
But he has no sons either
The princess herself had requested her disorder be made public, Kyodo news agency said.
"We will consider revamping her official duties," the Imperial Household Agency said.
In May, Prince Naruhito caused a stir when he accused the Imperial Household of denying Princess Masako the chance to lead a more varied life.
Doctors say Adjustment Disorder is manifested as depression or anxiety and is caused by a specific event which has brought on stress.
The Imperial Household Agency said that Princess Masako had received therapy and a small amount of medication, and was recovering, but still needed more time to rest.