Mikhail Piotrovsky, the museum director, told reporters on Tuesday, a day after reporting the thefts, that the items were not insured because they were in storage and that only exhibited artworks at the Hermitage are insured.
He added that the theft was believed to have been an inside job that probably took place over several years at the St. Petersburg museum.
He said: "It is clear that without the involvement of museum staff, this could not have happened."
The theft, which highlights the poor security at Russian cultural institutions, was discovered after a routine inventory check that began in October 2005 and was completed at the end of July.
The 221 missing items included a selection of medieval and 19th-century Russian jewelry, silverware and enameled objects.
Years can pass between inventory checks of specific collections in the more than 1,000-room museum, which has more than 3million pieces of artwork.
Piotrovsky said that only several hundred thousand of the 3million artworks at the Hermitage are registered in an electronic catalogue, and the museum spends only US$750,000 a year on security.