SOMERS, N.Y. — It’s every worker’s dream: take as much vacation time as you want, on short notice, and don’t worry about your boss calling you on it. Cut out early, make it a long weekend, string two weeks together — as you like. No need to call in sick on a Friday so you can disappear for a fishing trip. Just go; nobody’s keeping track.

That is essentially what goes on at I.B.M., one of the cornerstones of corporate America, where each of the 355,000 workers is entitled to three or more weeks of vacation. The company does not keep track of who takes how much time or when, does not dole out choice vacation times by seniority and does not let people carry days off from year to year.

Instead, for the past few years, employees at all levels have made informal arrangements with their direct supervisors, guided mainly by their ability to get their work done on time. Many people post their vacation plans on electronic calendars that colleagues can view online, and they leave word about how they can be reached in a pinch.

“It’s like when you went to college and you didn’t have high school teachers nagging you anymore,” said Mark L. Hanny, I.B.M.’s vice president of independent software vendor alliances. “Employees like that we put more accountability on them.”