PURPOSE To compare the treatable stromal bed area created by a temporal versus superior hinge laser in situ keratomileusis (LASIK) flap. SETTING Assil Sinskey Eye Institute, Santa Monica, California, USA. METHODS A randomized retrospective case review was performed of 2 subgroups (each with 12 eyes) of a cohort having LASIK for the correction of hyperopic astigmatism between August 2001 and March 2002. In 1 group, superior hinge LASIK was performed using the standard surgical technique for the 9.5 mm Hansatome suction ring. In the other group, the keratome was rotated 90 degrees such that a temporal hinge LASIK was performed with the 9.5 mm Hansatome suction ring. Corneal curvature (central mean keratometric value), flap diameter (arc length), and treatable stromal bed area were measured in each eye, and mean values were compared between the 2 groups. A treatable stromal bed area was defined as the circle centered over the entrance pupil, tangent to the hinge (devoid of hinge interference). RESULTS The mean keratometry and mean flap diameter in the superior and temporal hinge groups measured 42.3 diopters (D) and 9.68 mm and 42.2 D and 9.69 mm, respectively. These differences were not significant (P=.882 for average keratometry and P=.943 for flap diameter). The mean treatable stromal bed area in the superior versus temporal hinge group measured 44.14 mm(2) and 62.25 mm(2), respectively. The difference between the 2 groups was highly significant (P<.0001). CONCLUSIONS A large diameter, temporal hinge LASIK flap yielded a significantly greater area of treatable corneal stromal bed than a superior hinge flap. There are several clinical and theoretical advantages of optimizing stromal bed exposure for any given flap diameter.