Michael S. Jeffries, the former chief executive of Abercrombie and Fitch who was charged with running an international sex-trafficking ring, on Friday was found unfit to stand trial because of an Alzheimer’s diagnosis.

In a three-page order, Judge Nusrat J. Choudhury of the Eastern District of New York, wrote that Mr. Jeffries was “suffering from a mental disease or defect rendering him mentally incompetent.” Judge Choudhury also ordered that Mr. Jeffries be hospitalized for four months to observe whether his condition improves.

The ruling followed a letter filed last month by Mr. Jeffries’s lawyers, Brian H. Bieber and Alek Ubieta. They wrote that, based on the independent evaluation of three doctors, Mr. Jeffries, 80, had severe dementia and Alzheimer’s, which “ensures continued decline over time.” The condition meant Mr. Jeffries could not understand the charges he was facing, his lawyers wrote.