An estimated 30.4 percent of those community members are smokers, nearly double the 15.4 percent of the general population who smoke, said Brian Davis, project coordinator for Breathe California.
"There are a lot of reasons why LGBT people are more likely to start smoking," Davis said. "Young people growing up as LGBT face a lot more stress than other young people and are often outsiders and ... want to make a statement in opposition to society."
The event, called Butt Out, will feature a 10-foot-tall Grim Reaper who will be chased around the Castro District by rally participants.
Members of the LGBT community who smoke or have smoked will talk about health issues associated with smoking, Davis said.
The event begins at 5:30 p.m. at the corner of Castro and Market streets, and participants will have their faces painted to look like skulls at 5 p.m.