Almost 300 people waited 12 hours to be treated at emergency departments across Northern Ireland during December, figures have revealed.
The latest official statistics showed that 2,302 more people attended accident and emergency departments last month compared to the same period during 2014.
Between October and December nearly 800 people faced half-a-day's wait.
The number of patients waiting more than 12 hours - in breach of Government targets - jumped from 91 in December 2014 to 294 a year later.
The Ulster Hospital reported the most notable decline in performance, with the number rising from 45 to 162 people.
The latest blow comes after it emerged that the number of people waiting more than four months for a first outpatient appointment had soared by almost 1,500% in three years.
In September 2013, 6,923 people across the province were faced with an anxious wait of longer than 18 weeks for a test or consultation. By 2015 this had rocketed to 109,288.
Delays for people with suspected breast cancer were at the time described as "intolerable".
The Department of Health figures revealed that only 44% of women 'red-flagged' by their GP were seen within 14 days for a first assessment with a breast cancer specialist in the South Eastern Trust in September.
This came about as a result of that trust helping the Belfast Trust reduce its backlog in assessments.
Last November Health Minister Simon Hamilton set aside £40m to tackle the problem of huge waiting lists.
The money is being used to provide additional bed capacity, additional domiciliary care and nursing home placements as well as extra ambulance cover.
But former Health Minister Michael McGimpsey warned that Mr Hamilton's strategy was a "sticking-plaster" approach.
However, a Department of Health spokeswoman insisted that the shocking figures needed to be put into context. "In December there were almost 59,000 attendances at emergency departments, and just 0.5% of those people waited more than 12 hours for admission or discharge," she said.
"The number of 12-hour waits has reduced substantially in recent years compared to just five years ago when a number of months saw breaches of around 1,000.
"The minister has provided £8m to invest in additional measures to address the expected pressures over the winter period, including pressures in primary care.
"The funding is being used to support capacity in a number of areas including increasing diagnostic capacity, additional bed capacity to support anticipated increases in demand, additional domiciliary care and nursing home placements, additional GP surgeries in-hours, additional GP, nursing and call handler support out of hours, and additional ambulance cover."