Superior Court Judge Elden Fox, who met with defense and prosecution lawyers in his chambers, said Ryder was absent because of an "unusual" circumstance, but prosecutors did not say what the circumstance was.
"We'll be back in court tomorrow," said Sandi Gibbons, a spokeswoman for the Los Angeles County District Attorney's Office.
The judge also put off until Wednesday a hearing on a prosecution motion to drop a felony drug charge against Ryder.
Prosecutors said last week that Ryder's lawyers had provided information that she was not illegally possessing drugs when she was arrested in December 2001, for allegedly stealing $6,000 worth of merchandise from Saks Fifth Avenue in Beverly Hills.
The Oscar-nominated star of "Girl, Interrupted" and "Little Women" faces charges of felony grand theft, commercial burglary and vandalism. The drug charge was filed because police found some prescription drugs -- but no prescription -- in Ryder's bag.
In a prepared statement, the District Attorney's office said it filed a request to dismiss the drug charge after the defense turned over a sworn statement by a witness that, "if true, raises a question as to whether the defendant possessed the requisite criminal knowledge necessary" for an illegal drug possession charge.
Ryder was freed on $20,000 bail following her arrest last year. She pleaded innocent to all charges at a preliminary hearing in June, when prosecutors presented evidence they said shows Ryder stole the merchandise.
A store security officer testified at the hearing that she was looking through slats in a dressing room door when she saw Ryder clip security tags from two purses and stuff the purses into her shopping bag. The guard also said she saw Ryder try to remove anti-theft tags from two other purses -- and that the actress cut her finger and left a blood spot in the bottom of one of the bags.
Kenneth Evans, the head of security at the store, testified that six anti-theft tags that had evidently been cut off of merchandise were found hidden in the store the day after Ryder was arrested -- including three on which the cut marks matched items Ryder was holding when she was arrested.
After the preliminary hearing, Ryder's attorney Mark Geragos told reporters the prosecution witnesses "lied through their teeth." He characterized their testimony as "close to full-blown perjury."
He said Ryder didn't steal the merchandise she is accused of stealing, and he believes the store "targeted" her.
"I've got evidence that Saks targeted her," he said.
Geragos has also accused the Los Angeles County District Attorney's office of targeting Ryder because she is a celebrity.
Ryder -- who starred with Adam Sandler this summer in "Mr. Deeds" -- became a star in the 1980s with appearances in "Beetlejuice," "Heathers" and "Great Balls of Fire!" She was nominated twice for the Oscar -- for best actress in "Little Women" (1994), and best supporting actress in "The Age of Innocence" (1993).
Teacher apologizes for showing sexual image of herself in class
Scarlett Johansson steps out with fiance after pregnancy reveal