USinternetworking

Prospectus Summary

THIS SUMMARY MAY NOT CONTAIN ALL OF THE INFORMATION THAT MAY BE IMPORTANT TO YOU. YOU SHOULD READ THE ENTIRE PROSPECTUS, INCLUDING THE FINANCIAL DATA AND RELATED NOTES, BEFORE MAKING AN INVESTMENT DECISION. UNLESS OTHERWISE INDICATED, ALL INFORMATION IN THIS PROSPECTUS (1) ASSUMES NO EXERCISE OF THE OVER-ALLOTMENT OPTION TO PURCHASE ADDITIONAL SHARES OF COMMON STOCK GRANTED TO THE UNDERWRITERS AND (2) DOES NOT REFLECT A 1 FOR STOCK SPLIT WHICH WILL BECOME EFFECTIVE PRIOR TO THE CONSUMMATION OF THIS OFFERING. IN THIS PROSPECTUS, WE WILL REFER TO USINTERNETWORKING, INC. AND ITS SUBSIDIARIES, COLLECTIVELY, AS "USI," "WE" AND "US."