Amy Winehouse is being treated at the Priory Clinic and will remain there "on doctors' advice", according to her spokesman.
He said the 27-year-old singer is at the London clinic for "treatment" ahead of a series of European gigs next month but did not offer further details about the nature of the treatment she is receiving.
The Priory offers treatment for a range of psychiatric problems, as well as drug and alcohol addiction.
Her spokesman said: "Amy Winehouse has embarked on a treatment programme at the Priory Clinic.
"She wants to be ready for performances in Europe this summer and decided to seek an assessment. She will remain at the Priory on doctors' advice."
The star has had a high-profile battle with drink and drugs since finding fame in 2006 with her number one album Back to Black, but has succeeded in staying out of the public eye recently.
Her latest visit to the Priory is believed to have been suggested by her father, Mitch, over concerns she was drinking too much ahead of her tour.
In October last year, Winehouse claimed she had been drug-free for three years.
She told Glamour Magazine: "I'm much healthier now. I used to use drugs and I haven't used drugs in almost three years. It's not a hard thing."