Many people in the UK are unable to identify the location of their major organs, a study suggests.
A team at King's College London found public understanding of basic anatomy has not improved since a similar survey was conducted 40 years ago.
Less than 50% of the more than 700 people surveyed could correctly place the heart, BMC Family Practice says.
Under one-third could place the lungs in their correct location, but more than 85% got the intestines right.
There are concerns that a poor grasp of anatomy could potentially compromise patient care.
The researchers asked more than 700 people to look at outlines of both a male and female body and identify which of several shaded areas was a particular organ.
Those asked included apparently healthy members of the public and then people undergoing treatment for a problem that affected specific organs.
Even those for whom the organ was particularly relevant often performed poorly - more than half of those with renal problems did not correctly identify the kidneys.
Fewer than 30% of the general population were able to do so.
But liver patients did better, with 75.3% identifying the organ compared with 46% of the general population.
The researchers said they had aimed to update a similar piece of research carried out in 1970, in which just over half of all the questions were correctly answered.
But with an average of 52.5% correctly answered, the results have barely changed.
"We thought that the improvements in education seen since then, coupled with an increased media focus on medical and health-related topics and growing access to the internet as a source of medical information, might have led to an increase in patients' anatomical knowledge," said lead researcher John Weinman.
"As it turns out, there has been no significant improvement in the intervening years."
There was little difference between men and women, although women did perform better when a female body image was used.
Unsurprisingly, the better educated identified more organs correctly.
The researchers said their findings did raise concerns about doctor-patient communication and possibly therefore the quality of care.
Don Redding, head of policy at the Picker Institute Europe, a patient research group, agreed.
"There is a real problem with health literacy - people's ability to understand and process health information - which this study is indicative of.
"It really does matter, particularly as we look ahead to an NHS where resources are ever tighter.
"If people are going to use the NHS in an effective way they need to be able to communicate and understand what is said to them - this way we avoid repeat referrals, unnecessary hospitalisations.
"Everyone involved has to think harder about how to engage people in their own health - it's the only way."
Ellen Mason, from the British Heart Foundation, said: "Ideally the public would have a better knowledge of the location of their major body organs than this study suggests.
"This would hopefully produce a more meaningful dialogue with their doctor when something goes wrong with one of these organs.
"However, it is ultimately more important to know how to look after your heart than where it is in your body."
Answers: Heart - C, Kidneys - D, Pancreas - B.