Lindsay Lohan and Paris Hilton. Photo Credit: Scott Doctor / Splash News/File

Lindsay Lohan, who checked into a rehabilitation centre during January, was spotted partying with her friend Paris Hilton last weekend.

The outing to Les Deux nightclub on Friday night is the latest in a series of incidents that has prompted fears the 'Mean Girls' actress isn't taking her treatment seriously.

Earlier in her rehab stint, the actress had been seen out having lunch with friends and shopping.

On Saturday night she was seen leaving Area, a nightclub in West Hollywood, alone.

Lohan, who is 20 years old and therefore unable to drink legally in the US, has caused other residents in the rehab facility to complain that she's getting preferential treatment and using the venue as a hotel rather than a treatment centre.

The actress' representative, however, brushed off criticism last week.

"Lindsay is 100 percent not getting special treatment," said her rep Leslie Sloane Zelnik.

"This isn't the Betty Ford clinic, it's not a lock-down facility. There is personal time."