EXHIBIT 21 SUBSIDIARIES OF MOBILE MINI, INC. NAME OF JURISDICTION OF PERCENT SUBSIDIARY INCORPORATION/FORMATION OWNERSHIP BY MMI ---------- ----------------------- ---------------- Mobile Mini I, Inc. Arizona 100% Delivery Design Systems, Inc. (1) Arizona 100% Mobile Mini, LLC California 100% Mobile Mini, LLC Delaware 100% Mobile Mini of Ohio LLC Delaware 100% Mobile Mini Holdings, Inc. Delaware 100% (1) An inactive corporation. NAME OF JURISDICTION OF PERCENT SUBSIDIARY INCORPORATION/FORMATION OWNERSHIP ---------- ----------------------- --------- Mobile Mini Texas Limited Partnership, LLP Texas 99% - Mobile Mini Holdings, Inc. 1% - Mobile Mini I, Inc. 52