Scientists believe that the use of x-rays to aid diagnosis causes hundreds of extra cancers each year in the UK.
Tight rules govern when x-rays should be taken
Researchers from Oxford University and Cancer Research UK believe that about 0.6% of total cancer risk may be due to exposure to x-rays in hospitals.
Experts say that doctors should avoid "unnecessary" x-rays and CT scans.
However, the benefits of x-rays still outweigh the risks, say doctors, allowing serious medical conditions to be detected and monitored.
Worldwide, x-rays account for approximately 14% of the general population's exposure to radiation from both man-made and natural sources.
The cancer risk from cumulative radiation exposure can be quantified using data taken from those exposed to radiation after the 1945 atomic bomb blasts at Hiroshima and Nagasaki.
The proportion of cancers deemed to be caused by x-rays varies widely from country to country, says the report, published in the Lancet medical journal.
In the US, approximately 0.9% of cancers were due to diagnostic x-rays, in Germany, 1.3%, and the highest, at 2.9% in Japan, causing more than 7,500 cases a year.
It is not clear whether these risks are entirely due to a greater use of x-rays in medicine.
In the UK, studies have suggested that up to 30% of chest x-rays are not actually medically necessary, as are some CT body scans.
Dr Peter Herzog from the Ludwig Maximilians University in Munich said: "A general goal must be to avoid unnecessary x-ray procedures.
"Unnecessary CT examinations can lengthen hospital stay as well as causing radiation exposure.
"In everyday practice, those ordering radiological procedures should think carefully about the benefit for and the risk to their patients for each examination."
However, he was keen to point out that the benefits of x-rays were immense.
"They include the earlier detection of cancers by radiological examinations and the possibility of early treatment, which probably allows more cure of cancers than radiological exposure is able to cause."
Professor Adrian Dixon, an honorary consultant radiologist at Addenbrooke's Hospital near Cambridge, stressed that the benefits of x-rays far outweighed the risks.
He said: "We have very strict regulations to make sure we are only giving x-rays and CT examinations to those who need them."