The Patient and Client Council supported almost 1,000 people through the health and social care process last year, it has been revealed.
This represents a 12% increase in the organisation's workload over the last year.
Poor hospital care was the main subject of complaint, including access to and quality of care and treatment.
Other issues raised surrounded GPs, social care, mental health, dental services and nursing homes.
The Council helps make patients' voices heard within health organisations and published the figures in its annual report for last year.
Chief executive Maeve Hully said: "While many people have had a positive experience of dealing with the health and social care system, it is clear from the experiences of the people who have used the services that sometimes the health and social care system can be difficult to navigate and the nature of their complaints can be complex."
In 2011/12 the Council helped 980 people through the complaints process, a 12% increase in workload compared with the previous year.
The overall number of cases remains fairly static, at around 5,000.
The annual report said: "It is clear from our workload that patients, service users and their families want to be heard and increasingly seek support from the Patient and Client Council complaints service.
"Service improvements have been made as a result of the issues raised."