Background: The tissue-suture interface remains the weakest aspect of a rotator cuff repair, highlighting the importance of identifying techniques to improve stitch strength. Choice of suture-passing devices, size of the tissue bite, and stitch configuration are variables that may influence stitch strength and therefore repair stability. Purpose: To evaluate the effect that size of the tissue penetrator device and tissue bite size have upon the holding strength of commonly used stitches. Study Design: Controlled laboratory study. Methods: Three different-sized tissue-penetrating devices, small circular, midsized circular, and large rectangular, were used to place sutures in 192 infraspinatus tendon grafts of sheep. Tissue bite sizes of either 0.5 cm or 1.0 cm for 4 different stitches, a simple, mattress, modified Mason-Allen (MMA), and massive cuff (MAC) stitch, were tested. Grafts were cyclically loaded and then loaded to failure. Mixed multivariate regression analysis was used to test the effect of instrument, bite size, and stitch configuration on peak-to-peak displacement, cyclic elongation, and load to failure. Results: The average ultimate load to failure with the smallest penetrating device was 112 N, significantly higher than with both the midsized (95 N) and large devices (91 N) (P<.001). The average load to failure was 31 N higher for a 1.0-cm bite size when compared with a 0.5-cm bite size (P < .001). The largest load-to-failure differences were found with the type of stitch placed: simple, 48 N; mattress, 69 N; MMA, 130 N; and MAC, 152 N (all P < .02). For simple and mattress stitches, each additional pass of the suture increased the load to failure by 21 N. In MMA and MAC stitches, an additional pass resulted in an increase in the load to failure by 50 N. Cyclic elongation did not differ by instrument type (all P >.5). The elongation of stitches with a 1.0-cm bite size was 0.14 mm higher than stitches with a 0.5-cm bite size (P < .001). No meaningful difference in peak-topeak displacement was seen for bite size, instrument type, or stitch construct. Conclusion: The strength of rotator cuff stitches was significantly affected by the different-sized tissue-penetrating instruments and size of the bite. However, the greatest predictor of time-zero stitch strength is the type of stitch placed. © 2013 The Author(s).