The Strathclyde Gay and Lesbian Switchboard (SGLS) which was set up in 1977 above a Chinese restaurant in Union Street, Glasgow to provide information, advice and one-to-one communication for the region's gay community, will shut on Hogmanay.
The charity said its major supporter NHS Greater Glasgow and Clyde decided funding should end two years ago – and have survived on savings since.
Another health board, which makes up 22.9% of its funding, also had to drastically cut the £7500 annually it normally provides.
SGLS co-ordinator director David Thomas said: "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."
In the late 1970s and during the 1980s volunteers handled an enormous volume of calls amid growing fears about over the spread of HIV and Aids. In subsequent decades campaigns such as Keep the Clause – against the repeal of Section 28 – and concerns about homophobia kept the helplines busy.
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."
NHS Greater Glasgow and Clyde said it ceased funding as it was already funding two other groups providing a similar service.