Patients under the age of 75 attending Tallaght University Hospital's emergency department faced average waits of 21 hours in April to be admitted, HSE figures show.
And last month, those aged over 75 waited an average of 19.3 hours before being admitted.
So far this year, eight elderly patients waited over 48 hours in the emergency department.
The wait times are the worst of all Dublin hospitals, with the exception of St Vincent's where over 75's faced average waits of 21.6 hours.
Read more: HSE official calls for calories on restaurant menus to tackle 'obesity epidemic'
Dublin South West TD Sean Crowe said the issue of overcrowding has "reached a new extreme".
“The most shocking revelation in the figures was that over 200 patients over 75 had to wait more than 12 hours for admission in TUH already this year," he said.
“This is no way to be treating our older citizens. Eight people over 75 had an admission time of over two days and TUH is only one hospital. No Health Minister should be able to stand over that.
“Patients have been suffering the torturous consequences of overcrowding for years, but these figures show that the problem has reached a new extreme.
“The HSE target is all patients are to be admitted within 6 hours. Only 1 in 9 patients over 75 were seen in less than six hours in TUH this year.
“12+ hour waits in emergency departments are unacceptable for any patient, but especially for elderly people who are often presenting with complex and multiple health needs, as well as mobility issues."
A spokeswoman for Tallaght University Hospital told Dublin Live that their Emergency Department is "exceptionally busy" this year.
She said: "In the month of April our 8am Trolley count was up 72% when compared with the same period last year. The number of people presenting to the department are up 7% for the first four months of the year.
"Of particular note is the number of patients over 75 years of age being admitted which was up 19% when compared to the first four months of the year.
"One of the major contributing factors leading to delays in the ED is a shortage of beds in the Hospital. The number of patients over 75 yrs. attending the ED is up considerably in the first four months of this year. This age group have an admission rate of 60% and often need a longer length of stay.
"They also need a higher discharge support need. Their discharge from the Hospital continues to be a challenge with a high number of patients waiting home care packages or a place in a nursing home."
The spokeswoman explained measures the hospital is taking to combat long Emergency Department waits.
She said: "With regard to what we are doing about this, the Hospital works continuously to free beds for admitted patients, but there is a clear underlying requirement to develop additional onsite bed capacity.
"Following completion of an external strategic analysis review we are currently in discussions with the HSE to develop a new 72 single bed facility at the Hospital to address these additional capacity requirements.
"We are also developing an offsite GP pathway to reduce the waiting time for patients who do not need to be in an ED for their medical care."
Read more: Kind-hearted Dublin dentists offer free care to Ukrainian refugees
Sign up to the Dublin Live Newsletter to get all the latest Dublin news straight to your inbox.
