Thousands of patients were waiting for routine treatment at Hampshire and Isle of Wight Healthcare Trust in October, new figures show.
It comes as Health and Social Care Secretary Wes Streeting warned there is still "a long way to go", despite waiting lists across England starting to fall.
NHS England figures show 3,838 patients were waiting for non-urgent elective operations or treatment at Hampshire and Isle of Wight Healthcare NHS Foundation Trust at the end of October – up from 3,420 in September.
Of those, one had been waiting for longer than a year.
The median waiting time from referral to treatment at Hampshire and Isle of Wight Healthcare Trust was five weeks at the end of October – down from seven weeks in September.
Nationally, 6.3 million people were waiting to start treatment at the end of October – in line with the end of September.
Tim Gardner, assistant director of policy at think tank the Health Foundation, said the figures show the substantial challenge the Government faces.
He said: "Whilst promising progress has been made in recent months, the 18-week target hasn’t been met for nearly a decade.
"With the NHS facing the prospect of a very difficult winter, making further headway over the next few months will be very tough."
Mr Gardner added once the winter is over the Government should focus on addressing inequalities in health across the country.
Separate figures show 1.6 million patients in England were waiting for a key diagnostic test in October – the same as in September.
At Hampshire and Isle of Wight Healthcare Trust, 2,367 patients were waiting for one of nine standard tests, such as an MRI scan, non-obstetric ultrasound or gastroscopy at this time.
Of them, 80 (3%) had been waiting for at least six weeks.
Other figures show cancer patients across England are not being seen quickly enough.
The NHS states 85% of cancer patients with an urgent referral should start treatment within 62 days.
But NHS England data shows just 67.3% of cancer patients urgently referred nationally began treatment within two months of their referral.
That was down from 69.2% in August.
Danielle Jefferies, senior analyst at The King’s Fund, said the NHS is facing "a long list of priorities" across services, including reaching the 18-week waiting times target.
She added the way the NHS's performance is assessed should be reviewed to include a wider range of services and prompt reform.
Ms Jefferies said: "Winter pressures impact on all parts of the NHS and social care.
"How the health service is faring cannot just be measured by what is happening in hospitals — a true assessment must look at the care patients need from community and primary care services.
"Many people are struggling to access GP appointments and unable to get the support with social care services they need.
"There should be a more wide-ranging review of performance targets to shine a spotlight on these services and incentivise much-needed reform of the health service."
Health and Social Care Secretary Wes Streeting said: "Since the general election, we have been ramping up to delivering the extra two million appointments a year, ending the strikes and investing more in the health service.
"As a result, the NHS today is delivering a record number of treatments and waiting lists have begun to fall.
"There’s a long way to go, but through our plan for change we will get patients seen on time again."