Poor mental health is evident in about two-fifths of Europeans, researchers have said.
A large-scale study involving people from 30 countries in Europe, including the UK, showed that 38.2% of people have some type of psychological disorder, with many not even receiving treatment for their condition.
The most common health problems are anxiety, insomnia and depression, said the scientists at Dresden University of Technology in Germany where the research was carried out.
The rate of illness has not increased since 2005, but neither has any improvement been noted in the number of ill people given treatment since then.
The scientists said only about one in three people with poor mental health get treatment.
According to one of the research leaders, Professor Hans Wittchen, rates of ill health are more or less the same for women and men but the specific conditions are different for each sex. For example, women are said to be two-and-a-half times more likely to be depressed than men, especially during years of having children.
Overall, the rate of depression recorded among women is about double that of the 1970s.
The research involved about 514 million people and included both anxiety and bipolar disorders, insomnia, depression, schizophrenia and addiction. The study findings were published by the European College of Neuropsychopharmacology.