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ABSTRACT: The paper reviews the causes of under-estimation of the long-time future deflections of large-span prestressed concrete box girder bridges. Six causes are discussed: 1) wrong creep and shrinkage model; 2) obsolete creep analysis method; 3) ignoring randomness; 4) lack of model updating based on short-time tests; 5) wrong tendon layout; and 6) neglect of shear lag. The present paper focuses on the last two causes, while a brief review of the other causes is planned for the conference presentation. So is a discussion of why the record-span Koror-Babeldaob Bridge in Palau deflected 1.1 m more than expected in design. 1 INRODUCTION It has frequently been experienced that the box gird-ers of many prestressed concrete bridges deflected far more than predicted in design. The deflection evo-lution has often been counterintuitive, with slowly growing or negative deflections in the early years, followed later by a rapid and excessive deflection growth. Six different causes of these problems may be discerned