A review has revealed that 89 people received an "unacceptable" level of care in hospital or the community in the days before they died.
The review, which involved 381 patients, showed a further 119 people could have had better care.
Doctors – who have written to the relatives of the patients involved – have now apologised for the poor quality of the service provided.
Dr Kevin Harris, medical director at University Hospitals of Leicester NHS Trust, and Professor Mayur Lakhani, chairman of West Leicestershire clinical commissioning group, said: "We have let some people down.
"We want to apologise to the families of all 89 patients whom the review found to have received substandard care and assure them we are going to work tirelessly with our colleagues to make substantial and lasting improvements to the health system."
The review was commissioned by all NHS organisations in Leicester, Leicestershire and Rutland – after figures showed death rates for Leicester's hospitals were slightly higher than normal – to see where improvements might be made.
Dr Harris said the death rate might have been affected by a high number of people close to the end of their lives being admitted to hospital because no other support was available.
Dr Harris said: "This is about improving care, not about saving lives. The outcome would not have been different for any of these patients."
The review was conducted by Dr Ron Hsu and Lucy Douglas-Pannett, public health experts from the University of Leicester.
It focused on 381 patients admitted as emergencies to Leicester Royal Infirmary, who then died in hospital or within 30 days of discharge, between March 2012 and June 2013.
The authors said: "While the reviewers found cases of excellent care... there was a worryingly wide variation in care which included care considered to be 'unacceptable'.
"There was evidence of fractured care, dysfunctional processes and lack of joined-up thinking throughout the NHS in Leicester, Leicestershire and Rutland."
Most of the issues related to confusion over do not resuscitate orders – where a patient was resuscitated when they should not have been or where it would have been better not to resuscitate them.
Other issues related to clinical assessment by GPs and hospital doctors, palliative care – where patients had tests or investigations which, given their prognosis, were not appropriate – and delays in prescribing antibiotics.
Dr Harris said there had not previously been "such an exhaustive study of the whole patient journey from primary to secondary and intermediate care".
He said: "We set out to find problems and we found them, so we are now better positioned to address those system-wide issues."
Of the 89 found to have received substandard care, 79 involved city hospitals, 25 primary care and 15 community or social care.
Prof Lakhani, a Sileby GP, is heading a task force with Dr Harris to make changes, and said care provided out of hospital had to improve.
Karen Chouhan, spokeswoman for Healthwatch groups in Leicester, Leicestershire and Rutland, said: "We hope to see swift and decisive action, rather than further unnecessary information gathering."
Leicester deputy mayor Councillor Rory Palmer and Councillor Ernie White, cabinet member for public health at Leicestershire County Council, said the review reiterated the need for a joined-up health system.
Coun Palmer said: "This report is going to be distressing and upsetting for families."
Coun White said: "Lessons are being learnt and care will improve."
Leicester West MP Liz Kendall said staff must be trained properly and communication be improved.
A Leicester Mercury Patients' Panel spokesman said it was vital various health providers listened to one another.
