The Strathclyde Gay and Lesbian Switchboard (SGLS) which was set up on Union Street, Glasgow, in 1977, will shut on Scotland’s Hogmanay (New Years Day).
The charity said its major contributor, NHS Greater Glasgow and Clyde, cut funding two years ago leaving SGLS surviving on savings since.
Another health board recently also scrapped its funding.
The service provides information, advice, arranges support meetings and one-to-one communication for the region's LGBT community.
It also runs an additional lesbian and transgender help lines, and runs a social support group called ‘icebreakers’.
SGLS co-ordinator director David Thomas told the Glasgow Herald: ‘Changing times, improvements in health promotion, the application of equality duties due to legislation changes and some shrinkage in funding meant all funders had to ensure they targeted their funds at those services which can have maximum impact on the health area being tackled.
‘In the case of Glasgow our type of support service is viewed as covered by the in house counselling service delivered by professional counsellors’.
The pioneering service helped people with coming out during the 70s, and counselled many issues as safer sex and HIV when the subject was a taboo.
It also counselled callers on issues of homophobia, particularly during the campaign against repealing Section 28 in Scotland.
In a statement, the SCLS said: ‘With homophobia, bullying and discrimination still highly prevalent, it's clear why a service such as SGLS is needed.’
The service will shut on the 1 January 2013.