A team at University Hospital in Essen, Germany, followed 158 transgender women patients for a median of more than six years after their surgery. They found approximately 75 percent of patients showed improved quality of life after their procedure. The results were unveiled last month at the annual European Association of Urology Conference in Copenhagen.

“It’s very important that we have good data on quality of life (QOL) in transgender people,” Dr. Jochen Hess, the study’s lead author, told NBC News. “They generally suffer from a worse QOL than non-transgender population, with higher rates of stress and mental illness, so it’s good that surgery can change this, but also that we can now show that it has a positive effect.”

The study’s subjects were transgender women aged 18 years or older, with a mean age of 50, who had undergone gender-affirming surgery at the University Clinic in Essen between 1995 and 2015.