Gaga went topless save for marijuana-leaf pasties (she also wore them stuck to her face), a long ivy-green wig and a matching tulle skirt adorned with mini marijuana leaves, reported People magazine.
She also wore a crown adorned with marijuana leaves at the party in Puerto Rico.
"I love you guys so much. Had such a blast tonight. The show, the rumba afterward. Puerto Rico knows how to have fun. I love my fans... I was weed for halloween. Best costume ever its so fun. Princess High the Cannabis Queen," Gaga tweeted.