What is the test for a judge's discretion on costs in a personal injury action?

Great deference is owed to an award of costs. The exercise of a judge’s discretion on costs cannot be disturbed on appeal absent an error in principle or if the costs order is plainly wrong (Hamilton v. Open Window Bakery Ltd., 2004 SCC 9 at para. 27, [2004] 1 S.C.R. 303).

Although a judge enjoys wide discretion in imposing costs, that discretion must be exercised judicially (i.e., not arbitrarily or capriciously). That discretion includes the ability to depart from the applicable tariff when the judge considers an award of costs according to the tariff to be unsatisfactory. Rothstein J.A. (as he then was) explained in Consorzio Del Prosciutto Di Parma v. Maple Leaf Meats Inc., 2002 FCA 417 at para. 10, 297 N.R. 135, that the discretion to depart from the applicable tariff on an award of costs “should be prudently exercised.”