Health Secretary Patricia Hewitt has admitted there is "still more work to do" on a Labour 1997 election pledge to end mixed-sex hospital wards.
An investigation by the health service's chief nurse found that parts of the NHS are still failing to keep men and women separate.
One in six NHS hospital trusts - 28 out of the 172 in England - are struggling to provide single-sex accommodation.
Campaigners said mixed-sex accommodation denies patients treatment with "privacy, respect and dignity".
The Conservatives accused Labour of trying to "bury bad news" by releasing the report on the day Prime Minister Tony Blair is expected to announce his leaving date.
The inquiry came after patients questioned claims by ministers last November that just 1% of patients were being seen in mixed-sex wards.
Katherine Murphy, of the Patients Association, said a succession of ministers have broken promises to end mixed-sex wards over the past 10 years.
She said: "Patients have a right within the NHS to be treated in a safe environment with privacy, respect and dignity."
Ms Hewitt said: "The NHS overall has an excellent record of treating people with dignity and respect. Year after year, surveys show that the overwhelming majority of patients feel they have their privacy respected and they receive good care.
"However, this report shows there is clearly still more work for the NHS to do to meet our commitment to eliminate mixed-sex accommodation wherever possible."
