The hospital group which oversees Our Lady of Lourdes Hospital in Drogheda has admitted that patient information was found "outside the grounds of the hospital".
It follows a report of hospital patient notes being found in a garden in Drogheda earlier this week.
RCSI Hospitals said in a statement: "A report containing patient information was located outside the grounds of Our Lady of Lourdes Hospital, Drogheda by a member of the public.
"This member of the public contacted the Hospital and the report has been returned. The Data Protection Commissioner has been made aware of this.
"All patients have been notified. An investigation is underway."
Earlier: Senator calls for investigation after hospital patient notes discovered in Drogheda garden
Labour Senator Ged Nash is calling on the Data Protection Commissioner to investigate the discovery of hospital patient notes in a garden in Drogheda earlier this week.
This was the latest in series of data breaches, that he is aware of, he said, at Our Lady of Lourdes Hospital Drogheda.
Mr Nash told RTÉ radio’s Morning Ireland that he was contacted on Monday by a constituent who lives a kilometre from the hospital, who found the notes during a clean up of their garden.
Mr Nash said the notes, containing details of ten patients who attended the hospital on April 11, were returned to the hospital when a member of staff called to the home of the woman who had found the notes.
"The Data Protection Commissioner needs to investigate this very urgently because this is not the first time that confidence in data management at Our Lady of Lourdes hospital has been affected and confidence, of course, in the context of these files is very important," said Mr Nash.
He said that the hospital acted quickly after it was contacted and had apologised to the woman who found the notes.
The next steps are very important, he said. Patients need to have confidence in the management of the hospital.
Mr Nash urged the hospital to contact and apologise to the patients concerned.
"Patients need to have confidence in the management of the hospital. The reality as well is that, because this is such a serious violation, these individuals and their families need to be contacted, need to be met personally by senior hospital management to explain what happened and to be assured it will never happen again," he said.
RCSI Hospitals have been asked for comment.