This year is no different since it's the first time sales of recreational weed are legal.
MAP: Where is weed legal?
Rolling a joint and lighting it up is the norm on 4/20. "Everyone sparks it up," said Eric Polk of Sacramento. He's been coming to Hippie Hill the past few years.
The ritual that has new meaning now that the sale recreational weed is legal in the state.
In the crowd of nearly 20,000 people, you'll find those who've been coming for years as well as first timers. "We're just here for the good vibes, nice weather, day in the city," said Kristen from Walnut Creek.
VIDEO: Bigger crowds expected at SF's 4/20 celebration now that cannabis is legal
Since 4/20 fell on a Friday this year, event organizers expect to surpass last year's attendance of at least 15,000 people. "We doubled up security. We beefed up our cleaning crew," said organizer Alex Aquino.
The event hasn't gone off completely without a hitch. At least half a dozen people were taken by ambulance as they required medical attention.
RELATED: At least 12 taken to hospital during 4/20 in San Francisco
SKY 7 was over the scene as paramedics assisted two people in the middle of a large crowd. Most of them were responsive as they were being carried out.
Despite these issues, people say the event is more organized. "Everything is more organized, there's actually gating around the area of the festival, that's a little different," said Polk.
Once the smoke clears the air, the massive cleanup will get underway and the party will be over.
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In the last 30 minutes, we've seen 4 people receive medical attention at Golden Gate Park. 3/4 people were conscious as they were being taken by paramedics. @abc7newsbayarea #hippiehill #420day #abc7now pic.twitter.com/gk6I0WpzLX— Carlos Saucedo (@Carlos_Saucedo) April 20, 2018
One person being taken in a stretcher to the hospital. Friends of patient tell me he collapsed at Golden Gate Park but is conscious and expected to be okay. @abc7newsbayarea #abc7now pic.twitter.com/Od3RScDZSJ— Carlos Saucedo (@Carlos_Saucedo) April 20, 2018