Ombudsman Emily O'Reilly has described 2011 as the "busiest year in our history".
At the launch of the office's annual report today, she said over 4,200 complaints were dealt with out of 11,000 inquiries.
Among the cases was one involving Crumlin Children's Hospital, which launched an investigation into the parents of a child with apparent injuries they suspected were from physical abuse.
It later transpired the injuries were caused by medical treatment at the hospital. The parents eventually received a written apology.
This was one of a series of complaints involving the Health Service Executive, which accounted for 25% of the work carried out by the office.
Complaints against the Department of Social Protection accounted for 31% investigated by the Ombudsman's office last year.
Speaking later on RTÉ’s News at One, Ms O'Reilly claimed that discretion is increasingly being used to deny people welfare benefits that they have previously been awarded.
She said this is causing people a lot of angst and distress.
Ms O'Reilly said the Government is entitled to axe schemes in line with its policies and her office has no issue with that.
But she told RTÉ that if people are being denied benefits, they need to be told why.
She said in cases that involve medical diagnosis, where there is disagreement, the decision has to be evidence based and should not be simply rubber-stamped without explanation.
Ms O'Reilly said all complaints were dealt with using reduced resources, and added it was important the public still had somewhere to turn to in relation to the public service.
She said she believed hers was an office the public could still trust to deliver.
