Letterkenny General Hospital tonight apologised to 16 patients whose personal details were found dumped, and has launched a full investigation.
The sheets of paper contained the names, dates of birth and hospital numbers of the people concerned as well as a medic's hand-written note.
Hospital officials confirmed they recovered the documents and were tonight trying to telephone all patients to apologise for the error.
Letterkenny Hospital Manager Sean Murphy said: "We apologise unreservedly to the patients involved and have this afternoon written to them.
"Where we were unable to contact patients by telephone, we will continue to try this evening and over the weekend."
Three pages of official hospital papers were discovered last night by residents in the the Bogside area of Derry.
Letterkenny Hospital said the clinician's hand-written notes on the sheets of paper were, in many cases, simply a single word or abbreviation.
"No other details regarding the patients' addresses, personal circumstances or medical history are contained," a spokesman added.
"A full investigation into the source of the three pages is currently under way at the hospital."
PA