Unicompartmental knee arthroplasty has gained popularity recently as a treatment for unicompartmental tibiofemoral non inflammatory arthritis. Tibial plateau stress fracture after unicompartmental knee arthroplasty (UKA) through guide pin holes placed in the proximal tibia has not been previously reported. In each case in this report, the compressive strength of the proximal tibia was reduced by the drilling of multiple holes for the placement of guide pins and holes for the lugs of the tibia component resulting in fracture through these holes between 3 and 18 weeks (median 8 weeks) post-operatively. In at least one case, the medial tibial cortex was violated by one pin. All cases required revision total knee arthroplasty (TKA). It is intuitive to caution against the use of multiple guide holes in the proximal tibia in UKA. If 3 or more hole pins are deemed necessary, surgeons must be aware of the potential for stress fracture and monitor patients accordingly. Peripheral pins that infract the medial tibial cortex should also be avoided.