Thousands of patients were waiting for routine treatment at Southern Health in June, new figures show.
The NHS is facing a difficult summer as overall waiting lists climb for a third month in a row.
NHS England figures show 3,927 patients were waiting for non-urgent elective operations or treatment at Southern Health NHS Foundation Trust at the end of June – up slightly from 3,921 in May, and 3,182 in June 2023.
None of those had been waiting for longer than a year.
The median waiting time from referral at an NHS Trust to treatment at Southern Health was six weeks at the end of June – the same as in May.
Nationally, 7.62 million people were waiting to start treatment at the end of June. This was up slightly from 7.6 million at the end of March and a third consecutive rise.
Health Secretary Wes Streeting said: "These figures confirm that 14 years of Conservative neglect left the NHS broken, waiting lists rising, and patients failed. Never again should the Conservatives be trusted with our health service.
"It will take time to turn the NHS around. But we are working night and day to get the NHS back on its feet, so it can once again be there for us all when we need it."
Separate figures show 1.6 million patients in England were waiting for a key diagnostic test in June – a fall from 1.7 million in May.
At Southern Health, 1,600 patients were waiting for one of nine standard tests, such as an MRI scan, non-obstetric ultrasound or gastroscopy at this time.
Of them, three 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% of cancer patients urgently referred nationally began treatment within two months of their referral.
That was up from 66% in May.
Louise Ansari, chief executive at Healthwatch England, said: "We are concerned that the progress made in speeding up both cancer diagnosis and the commencement of cancer treatment in recent months is slowing.
"Despite some progress on the referral to treatment target, the NHS is still falling well short of its operational target that 85% of patients wait less than two months between an urgent referral and treatment commencing.
"Urgent action is required to ensure that timely cancer diagnosis and treatment becomes the norm for all patients in England."
Professor Sir Stephen Powis, NHS national medical director, said the NHS could be in the middle of its "busiest summer ever".
He said: "While we have seen improvements in the number of patients seen and treated within four hours in A&E, slightly faster ambulance response times, and more than three quarters of cancer patients receiving an all clear or diagnosis in four weeks, it is clear that waits for patients across a range of services remain unacceptable and there is much more to do to deliver more timely care for those who need it.
"Nobody in the NHS wants to see patients experiencing long delays and we are committed to working with the Government to create a 10-year plan for health that includes a clear plan to bring waits down.”