Gay and lesbian patients are often reluctant to reveal their sexuality to their doctors because they fear their treatment will suffer, a report claims.
Doctors must not discriminate against gay men, the report says
A British Medical Association report also says some homosexual doctors do not 'come out' to colleagues because they fear the consequences.
One gay doctor even reported being told he should not work in child health because of his sexuality.
The BMA has issued guidance on how the NHS should combat discrimination.
Its report is published at the start of Gay Pride fortnight.
It follows the recent publication of legislation which outlawed discrimination on the grounds of sexual orientation.
The BMA says simple changes, such as using gender neutral language when talking about a patient's partner, and not assuming sexual health is the primary health need of gay patients, would reduce feelings of discrimination.
Its report calls for a series of measures including guidance on sexual orientation in NHS equal opportunities policies, and a crack-down on incidents of homophobia.
It also includes guidelines for teaching medical students how to act in a non-judgemental way towards gay and lesbian colleagues and patients.
'Respect and sensitivity'
Dr Vivienne Nathanson, the BMA's Head of Science and Ethics said: "Everyone has the right to be treated equally, regardless of their sexual orientation.
"Doctors and patients should feel safe and confident when they are in hospitals and surgeries."
Dr Sam Everington, co-chair of the BMA's Equal Opportunities Committee and Deputy Chairman of the BMA said: "Future doctors have a responsibility to their colleagues and patients.
"Sexual orientation should be included in the medical school curriculum and will help create a health service environment where all doctors can achieve their full potential and all patients be treated with the respect they deserve."
Dr Rachel Hogg, co-chair of the Gay and Lesbian Association of Doctors and Dentists (GLADD) said: "The NHS currently uses an estimate that at least 1 in 20 of the population are lesbian or gay - so an increased awareness that colleagues and patients may not be heterosexual is crucial to treating each other sensitively and respectfully."
Justin Varney, a public health doctor based in London, said the discrimination within the health service tends to be subtle.
"When I was a student, there were doctors who said 'you can't do paediatrics as a gay man'.
"It's not blatant. People don't come and say 'you shouldn't do this speciality if you're gay.
"They would tend to say 'this might not be the wisest career path for someone with your skills'."
A spokesman for the gay rights organisation Stonewall said the report backed up previous reports of discrimination in the NHS.
He added: "While lesbian and gay staff are now protected by employment law, patients often face discrimination too which is why Stonewall is calling for protection in terms of goods and services in the Equality Bill currently going through parliament."
Carol Baxter, of NHS Employers, said: "More needs to be done to help NHS staff to protect themselves and their colleagues from sexual orientation discrimination.
"We would like to see more NHS employers establishing staff support networks for lesbian, gay and bi-sexual employees where they can share their experiences of what works and what doesn┐t work.
"This will ultimately have an impact on the quality of care received by lesbian, gay and bi-sexual patients and their carers."