The number of complaints made against one health board and how these were dealt with is concerning, the public services ombudsman has said.
Between April 2016 and March 2017, there were 194 made against Betsi Cadwaladr – the second highest was 107.
Ombudsman Nick Bennett highlighted three of these incidents, all involving Ysbyty Glan Clwyd, Denbighshire.
A Betsi Cadwaladr spokeswoman said it takes all complaints seriously and they help it find ways to improve services.
There were 702 cases closed across Wales in 2016-17, with 194 complaints involving Betsi Cadwaladr, 107 from Abertawe Bro Morgannwg, 102 from Hywel Dda and 93 from Cardiff and Vale.
“I am concerned about both the volume and outcome of complaints against Betsi Cadwaladr University Health Board over the past 12 months,” Mr Bennett said.
He issued five health public interest reports about serious cases over the course of the year and three involved Ysbyty Glan Clwyd in Denbighshire.
In the first, Mr Bennett said Betsi Cadwaladr should pay £20,000 to the wife of a hospital patient who did not see a consultant for 12 hours and later died.
Another related to “fundamental clinical shortcomings” when a bowel cancer patient died after being admitted for surgery.
The third was about a patient with a potentially life-threatening cancer who waited four months for his first treatment after a “disturbing lack of urgency”.
Redress payments to people who complained in the Betsi Cadwaladr area between April 2016 and March 2017 amounted to £61,999 in a Wales-wide total of £115,430.
“While public services are facing unprecedented pressures, it is essential that lessons are learnt when things do go wrong,” Mr Bennett added.
“We have assigned an improvement officer to work alongside the health board and hope to see better complaint handling and learning as a result of that.”
Representatives of the board are also due to attend a health complaint handling seminar organised by the ombudsman next month.
A spokeswoman for the board said: “We maintain a close working relationship with the ombudsman’s office and we will continue to liaise with our assigned improvement officer to ensure we develop our complaints handling and learning processes further.
“We are also reviewing our patient experience and complaints procedures.
“We will be attending the All Wales Health Complaint Handling Seminar and look forward to the learning opportunities it will provide.”