The Scottish Public Services Ombudsman (SPSO) said the number of complaints it received about health increased 11.5 per cent from 1,237 to 1,379 in 2013/14.
Of those it went on to investigate, 55 per cent of health complaints were upheld, up 3 per cent from previous year.
The majority of complaints received - 913 - related to patients’ clinical treatment and diagnosis, with 128 about communication and staff attitudes and 75 about appointments and admissions, such as delays and waiting times.
The ombudsman also saw increases in complaints in other sectors it covers, including local government and further education.
In total it received 4,456 complaints - an increase of 8 per cent on the 4,120 in 2012/13.
Ombudsman Jim Martin said they believed health complaints could be increasing due to factors such as people becoming more aware of the complaints process, rather than services deteriorating.
“People are less reluctant to complain. They can find their way through the complaints process a lot easier than five or six years ago,” he said.
“I think people genuinely care very strongly to see their reports through.
“When they see from the reports that run that things actually get done and changed because of them, that makes a difference.”
Mr Martin said when people went to the ombudsman they tended not to be looking for compensation but for an acknowledgement that something had gone wrong and hoped it would not then happen to another family.
“That seems to be the main driver,” he said. “People care about the NHS in Scotland.
“The NHS is taking the complaints handling process more seriously.
“I am very encouraged by the work being done to streamline and improve their own complaints process.”
Mr Martin said the number of people going to the SPSO when they should have first gone through local complaints procedures was coming down, which was encouraging as it showed these complaints were being handled better.
A Scottish Government spokeswoman said: “We want everyone to be confident that they will get the best possible care and treatment from the NHS in Scotland.
“We expect NHS boards to thoroughly investigate complaints about their services and where improvements can be made, it’s vital that action is taken and lessons learned quickly.”