NEW YORK — Whitney Houston is back in rehab.

A representative for the superstar singer confirmed Monday that Houston is undergoing treatment. Kristen Foster says Houston is in an out-patient program for drug and alcohol treatment. She says it is a voluntary measure and part of Houston's "long-standing" recovery process.

The 47-year-old, one of the most successful singers in pop music history, has battled problems with drug addiction for years. But in 2009, as she released a comeback album, she declared herself healthy and clean.

However, her 2010 tour overseas was troubled: Houston cancelled some dates due to illness and received negative reviews from fans who were disappointed in the quality of her voice and performance. Earlier this year, she gave an uneven performance in tribute to cousin Dionne Warwick at music mogul Clive Davis' annual pre-Grammy gala.

It's unclear how long Houston will be in rehab or where she's being treated; Foster had no further comment. However, Houston has been visible recently: Last week, she sang on stage with Chaka Khan during Prince's concert in Los Angeles.