Eating disorder sufferers in England can wait for up to 182 days for mental health treatment, according to new NHS figures.
The average waiting time for adults in England can vary from 20 to 182 days depending on the Trust, BBC Breakfast found through Freedom of Information requests.
The eating disorder charity Beat said that early intervention was critical and called for more investment in mental health services.
Data from 41 of the 55 mental health trusts found that 1,576 people have waited 18 weeks to see a specialist since 2012. A total of 742 waited 26 weeks, while 99 waited a year.
Waiting times for outpatient treatment have risen by 120% in some areas over the past four years.
Some of the highest average average waits were in Manchester - 182 days - and Kent and Medway - 116 days.
However in Dorset, Dudley and north-east London the average wait was 20 days.
Manchester Mental Health and Social Care NHS Trust said waiting times were longer than it wanted.
A spokesman added: "If more services were commissioned, more services could be provided. The trust continues to work within tight funding levels and with increasing demand."
Five mental health trusts responded by saying they did not provide a service for people with eating disorders at all.
The Government introduced new targets for mental health last week but waiting times for adult eating disorder services were not included, according to the BBC.
The Department of Health told the BBC that it was working to cut waiting times by developing a pathway for treating adults with eating disorders.
The target is to have 95% of patients seen within four weeks, or one week, for urgent cases, by 2020.
A spokesman said: "People with eating disorders must get high quality care as early as possible - and while this is happening in some places, there is far too much variation.
"That is why we're investing £150 million to develop community services in every area of the country for children and young people, and have set a target for routine care to be available within four weeks, and urgent care within one week by 2020."