Minimally invasive unicompartmental knee arthroplasty has been increasingly popular for the past few years. Several short- and medium-term published reports have shown it to be as efficacious as open unicompartmental knee arthroplasty, with reduced morbidity. However, complications specifically related to the minimally invasive techniques are not well documented. We report 2 cases of stress fracture of the medial tibial plateau after unicompartmental knee arthroplasty with minimally invasive instrumentation. Awareness of this as a possible complication, with increased care in surgical technique, will help to avoid this problem.