There were more than five million cases of anxiety disorder in the UK in 2010, a new study has found.
People suffering from some form of anxiety numbered 8,195,000 or 18.7% of the UK population, according to the study published in the Journal of Psychopharmacology.
The cost of treatment, absence from work and special care related to anxiety disorders was estimated by the team of researchers at £9.8bn.
Cambridge University researcher Barbara Sahakian, who co-wrote the paper, said the problems could be triggered by modern living and worries over job loss or debt.
She said mental health disorders were more common in urban areas partly as a result of "the stress of urbanisation and the competitiveness".
She said the cost was linked to the fact that anxiety disorders tend to be long-term conditions.
Anxiety was one of 18 different conditions identified by the researchers costing an estimated £112bn a year to the country. These included dementia, mood disorders, sleep disorders and addiction.
Over 5.2 million people suffered from a sleep disorder in 2010 - 11.7% of the total UK population - more than those suffering from an addiction, which numbered just under 1.9 million or 4.16% of the population.
However, the most costly disorder was dementia at nearly £20bn a year, partly due to the need for nursing home care.
Psychotic disorders, including schizophrenia, were the second most costly disorder, at around £14bn a year.