Is a patent applicant obligated to disclose prior art references to the USPTO, even if the references are adverse to the patent applicant's position?

Although there is no legal duty to search, MPEP 2000 states that each individual associated with the filing and prosecution of a patent application, supplemental examination, or patent reexamination has a duty to disclose to the Office all information known to that individual to be material to patentability.  Thus, if you do perform a search yielding material prior art (even if the prior art discovered is adverse to the applicant's position), it must be disclosed to the USPTO.