Justin Bieber was overcome with sickness at his concert on Saturday night and it was not "Bieber Fever."
The 18-year-old singer vomited twice on stage in suburban Phoenix, where he kicked off his national tour.
The pop star left the stage after each episode but returned and even did an encore at his sold-out concert at the Jobing.com Arena in Glendale, Ariz.
Bieber's fans sang some of his songs while he was offstage and he later apologized for being sick.
Bieber later tweeted "Great show. Getting better for tomorrow's show !!!! Love u"
He later added: "And .... Milk was a bad choice!"
Bieber's 45-city "Believe" tour continued Sunday at the MGM Grand Garden Arena in Las Vegas.