A two-year-old boy with swine flu has died.
The infant, from the Republic, was receiving intensive care treatment north of the border, according to the Public Health Agency.
The PHA said, at the family's request, no further details of the case would be released.
"The Public Health Agency would like to extend its sympathy to the family of this child," said a PHA spokeswoman.
Information on whether the child had an underlying medical condition is not being released.
But the fatality will nevertheless put further pressure on the authorities to re-think the policy decision not to vaccinate all under-fives against the virus, something which was done last year. Only infants in "at risk" health categories are being vaccinated.
Northern Ireland's health minister Michael McGimpsey, who offered his condolences to the boy's family, said medical advisers remain of the opinion that the vaccination programme should not be extended.
"I have recently spoken to other UK health ministers about Northern Ireland's current flu picture. I have also spoken to Mary Harney, the Republic of Ireland's Health Minister.
"In addition, I have consulted with the Joint Committee on Vaccination and Immunisation (JCVI) about the particular circumstances here. They do not recommend extending the vaccination programme beyond the current at-risk groups."
It was later confirmed that a second youngster with swine flu, a 10-month-old baby boy, had died in the north.