The Southern Health and Social Care Trust "failed in its duty of care" towards an allegedly sexually abused child, the NI Ombudsman claims.
Ombudsman Tom Frawley said the service given by the trust "fell short" of expectations.
Figures released on Monday revealed that overall complaints were up 23% during the first half of 2011.
The health and social care sector was singled out as having more than doubled its number of complaints.
The ombudsman deals with complaints from people who claim to have suffered injustice because of maladministration by government departments, agencies and a wide range of other public bodies.
The latest figures show an increase in the number of complaints regarding health and social care from 75 to 117.
Mr Frawley said the case involving the alleged sexual abuse of a child was "all the more concerning given the nature of the allegation and the trust's statutory responsibility to safeguard children".
Statutory regulations breach
He said he had identified failings in adhering to required child protection procedures and in keeping sufficient records.
"I deemed this investigation so important that in addition to recommending a comprehensive apology and consolatory payment to the complainant (the child's mother), I recommended that the trust share the report with the Regulation and Quality Improvement Authority with regard to follow up action," he said.
The ombudsman also found that two separate GP practices were in breach of relevant statutory regulations after they struck patients from their practice list.
In both cases, the patients had received no warning they would be removed from the list or given any explanation of why they had not been told.
Mr Frawley also highlighted the case of an elderly woman suffering from dementia who was admitted to the Royal Victoria Hospital.
"The trust failed to utilise detailed nursing plans which would have led to more appropriate and importantly more effective communication with the patient and her relatives," he said.