A report obtained by the Evening Times has detailed a three-year cycle of complaints about the Langlands Unit at the Southern General.
It reveals repeated concerns over "poor nursing care" at the 150-bed unit, which also cares for young people with disabilities.
Other recurring complaints have included missing items, a lack of compassion among staff and poor communication with relatives.
Today health bosses apologised for the standard of care which had fallen short.
The report concludes that two separate investigations and repeated action plans had "not resulted in sustained service improvement".
The charity Age Scotland described the findings as "extremely concerning."
Large sections of the report, obtained under Freedom of Information legislation, have been blacked out by NHS Greater Glasgow and Clyde, which said the "redaction" was done to protect the identity of staff and patients who had disclosed information about the unit.
It said measures had been put in place in light of the report including changes to senior nursing staff and the recruitment of more nurses.
The unit has not yet been inspected by the Healthcare Environment Inspectorate (HEI) which monitors elderly care facilities.
After the Evening Times revealed the finding of the report to the HEI a spokesman said the report had provided "useful intelligence".
A spokesman for Age Scotland said: "This underlines the importance of the work being done by the HIE and the Care Inspectorate."
When the £11.6 million unit was opened in 2002 by then Health Minister Malcolm Chisholm, he said: "The Langlands Unit will provide first-class health services for older people and young physically disabled people in Glasgow well into the 21st century."
Rosslyn Crocket, NHS Greater Glasgow and Clyde (NHSGGC), Nurse Director, said: "Improving care for older people in NHS Greater Glasgow and Clyde is a top priority for this board.
"We would like to reassure readers that any failure to meet the high standards expected have been identified, are being addressed as a priority, and indeed progress has already been made.
"I am sorry the standard of care provided to some patients within this unit has fallen short of the high standards that our patients rightly expect and deserve and we have put in place a rigorous programme of improvements to address this.
"Since the report was produced a number of actions and improvements have been taken forward."