At the end of September, 16.3% (39,557) of patients were waiting more than a year for a first consultant-led outpatient appointment.
The Health and Social Care Board described the figures as "unacceptable".
A plan to tackle the delays is expected to be announced in January.
The latest Department of Health figures show a total of 243,141 patients in Northern Ireland were waiting for a first consultant-led outpatient appointment at the end of September.
That is 7% more (17,548) than at the end of June and 5.4% (12,516) more than at 30 September last year.
Analysis by BBC News NI Health Correspondent Marie-Louise Connolly
The fact that hospital waiting times are up comes as no surprise.
The number of people living longer and requiring specialist health services is increasing - but that is not matched by either funding or extra staff.
As with the rest of the UK, Northern Ireland has a shortage of specialist staff.
Take radiology - at the moment there are about 40 vacant radiologist posts. That has a massive knock-on effect when it comes to seeing people on time.
There is also a shortage of specialist orthopaedic surgeons - hence the number of people waiting for hip replacements and back surgery.
In January, the health minister is due to announce a plan as to how she envisages tackling hospital waiting lists.
That is expected to include a detailed strategy and additional dedicated resources.
But it is hardly likely that those resources will solve the problem.
Instead, the health service will have to do things differently, including consultants changing how they work and being prepared to allow GPs and nurses to share the workload.
In the Northern Health Trust for instance, dermatology consultants are being encouraged to view photographs of patients and their complaint rather than insisting on seeing everyone in person.
Something radical needs to happen to shatter this cycle of men and women waiting unacceptable times on lists.
According to targets set by the health minister, at least 50% of patients should not have to wait any longer than the recommended nine-week target.
More than two thirds of patients in Northern Ireland (167,250) were waiting more than nine weeks for a first consultant-led outpatient appointment, according to the latest Department of Health figures. That is a slight increase compared to the same time last year.
At the end of September, more than 70,000 patients were waiting to be admitted to hospital. That is an increase of 11.7% on last year.
New figures indicate that in the past year there has been a 5.4% rise in the number of people in NI waiting to see a health specialist for the first time.