A quarter of autopsies performed for coroners are of a poor or unacceptable standard, according to a report.
The report says many coronial autopsies are below standard
A study, asked for by the Royal College of Pathologists, examined 1,691 autopsies and found in 310 cases the cause of death given was questionable.
The study team called for a review of the system, saying many bereaved families were being "sold short".
The Royal College of Pathologists said the report highlighted the pressures many of its members were working under.
It is the first ever audit of autopsies in England, Wales and Northern Ireland.
The ages of people in the autopsies investigated by the National Confidential Enquiry into Patient Outcome and Death (NCEPOD) ranged from three days to 101 years.
The report called for better communication between coroners and pathologists and for standard procedures to be introduced.
Ian Martin, lead co-ordinator for NCEPOD, said: "Our hope is that the whole of the coronial system will be reviewed."
Mr Martin said a uniform system for the coronial autopsy procedure was needed.
One in four autopsy reports (436 of 1,691) judged as poor or unacceptable
Brain was not examined in one in seven cases (238)
Very elderly may not have been examined as carefully as younger subjects
Only 64% (121 of 188) of mortuaries could store fixed tissues and organs
"There needs to be clear instructions from the coroner to the pathologist that are written so they understand what the questions are from the coroner.
"A lack of communication leads to a poor standard of service for a large number of individuals who require autopsies."
He said the current autopsy fee of £87.70 was undervalued, and placed pressure on pathologists.
"We don't know what the average cost of a coroner's post-mortem is, but one has to recognise that the current fee is inadequate," he said.
"Autopsies are all different and some require more tests than others, which increases the costs. We need to be more astute as to the true cost."
Report author Pathologist Professor Sebastian Lucas said: "One in four [autopsies] is not done well and families are being cheated - sold short - and they don't know it."
He told the BBC the report showed there was "huge variation across the country in the standards of the way things are done".
Families, who "deserved the truth", were being given the wrong cause of death.
"Pathologists are trained pretty well, what happens is the system does not encourage good practice," he said.
Jane Hanna, director of charity Epilepsy Bereaved, said the report backed up its experiences with working with families who have experienced a sudden death.
"It's shocking that there are so many poor autopsies. Families place great trust in the coronial system, but at the moment the system is inadequate and the trust of the bereaved is misplaced."
A spokesman from the Royal College of Pathologists, which had asked NCEPOD to investigate autopsy practice, said it agreed "clearer lines of accountability, ongoing audit of performance and improved communication between pathologists, coroners and the bereaved were all needed".
He added: "The college does not condone 'cutting corners' in autopsy practice, but is aware of the pressures placed on many of its members by the current national shortage of suitably trained pathologists, and by other resource constraints.
"Our goal is to develop a coroner's service which is an effective partnership between legal and medical expertise and which is fit for purpose in the 21st century."
A draft Coroner Reform Bill is due to be placed before parliament by the Department of Constitutional Affairs following further consultation.