The troubled star made the decision after pictures and a video clip which showed her allegedly taking crack cocaine were released by The Sun newspaper.
Amy's record company said that the singer's planned appearance at the NRJ awards in France has been cancelled, though she is aiming to perform at the Grammy awards in February.
"She has come to understand that she requires specialist treatment to continue her ongoing recovery from drug addiction and prepare for her planned appearance at the Grammy awards," a statement from Universal Music said.
"Amy entered the facility by mutual agreement and continues to receive the full support of all concerned."
The label added: "Amy is the most talented and important musical artist of her generation and has made huge strides on her road to recovery. The label has always had the best interests of Amy at heart and has been guided by her family and doctors in the last few months as to the best direction to take."
Winehouse checked into rehab with her husband Blake Fielder-Civil following her dramatic drugs collapse last year, but she chose to leave just two days later and refused to return without her partner.