This results in half of all eligible lesbian and bisexual women never having had a smear test, they said.
The human papilloma virus (HPV), which causes most cervical cancers, can be transmitted through lesbian sex.
Cervical cancer charities say all women, no matter their orientation, should have regular cervical screening.
Lesbian, gay, bisexual and transgender (LGBT) groups say women regularly face barriers to accessing healthcare and can have poor experiences when they do.
For example, in a survey of lesbian, bisexual and other women who have sex with women, 36% said a doctor or nurse had assumed they were heterosexual.
The National LGBT Partnership says women also suffer in other ways - they are more likely to report a long-term mental health problem and more likely to binge drink than heterosexual women.
Joanna, 30, was told that she did not require a cervical screen test because she was a lesbian.
Although she was eventually tested, Joanna says: "I just felt she [the doctor] needed to be more knowledgeable on the subject."
Diane, also 30, said she received inaccurate information about whether or not she could benefit from cervical screenings.
She said: "My GP didn't advise me of my risk level, she just made a number of blanket statements."
But HPV is passed on through body fluids, like other sexually transmitted infections.
This means that oral sex, transferring vaginal fluids on hands and fingers, or sharing sex toys can all be ways of being exposed to HPV.
The charity Jo's Cervical Cancer Trust says all women, regardless of their sexual orientation, should have regular cervical screening.
"As HPV can be transmitted through skin-to-skin contact in the genital area, gay women are equally at risk of contracting HPV and experiencing abnormal cervical changes and, thus, should always attend when invited for cervical screening."
In a study of attitudes to cervical screening among gay and bisexual women in the north-west of England, carried out by the University of Salford in 2011, 37% of women questioned said they had been told they did not require a cervical screening test because of their sexual orientation.
What is cervical screening?
It is a test to check the health of the cells of the cervix, not a test for cancer.
Around one in 20 women's tests show some abnormal changes. Most of these changes will not lead to cervical cancer and the cells may go back to normal on their own.
However, in some cases, the abnormal cells need to be removed so they cannot become cancerous.
All women who are registered with a GP in the UK are invited for cervical screening:
§ Aged 25 to 49 - every three years
§ Aged 50 to 64 - every five years
§ Over 65 - only women who haven't been screened since age 50 or those who have recently had abnormal tests
Who gets cervical cancer?
It is possible for women of all ages to develop cervical cancer, although the condition mainly affects sexually active women aged 30 to 45.
The condition is much rarer in women under 25.
There are about 3,000 cases of cervical cancer diagnosed each year in the UK.
Do lesbian and bisexual women need cervical screening?
Yes - women should always be offered screening whether they are gay, straight or bisexual.
Sometimes, lesbian women have been advised by health workers that they do not need screening because they do not have sex with men.
But only women who have never had sex at all (with either men or women) may be advised that screening is not necessary.