"Childhood sexual trauma, risky health behaviours, smoking, a lack of positive support and negative social interactions pose more of a risk for people's mental health than their sexual orientation," said lead researcher Richard Burns from Australian National University (ANU).
He said homosexual and bisexual people were more likely to experience these mental health risk factors than heterosexual people.
The study followed about 5,000 adults over eight years as part of the Personality and Total Health Through Life Project.
"We concluded that all things being equal that there is no particular mental health risk for people with a homosexual or bisexual orientation," he said.
"Our findings emphasise the importance of using longitudinal data to estimate long-term mental health risk associated with sexual orientation," he added.