Polat AE, et al. - One hundred four patients to whom medial unicompartmental knee arthroplasty (UKA) was applied between 2011 to 2016 with a minimum of 2 years follow-up were recruited in this study by the researchers in order to assess and contrast the functional outcomes and complication rates of patients in short-term and midterm follow-up period when medial UKA-applied patients were grouped according to BMI values. Of 104 patients, the average BMI was 34.4. Twenty-six, 40, 38 of these, were normal or overweight, obese and morbidly obese, respectively. Nonetheless, in these BMI groups, no important variation between the preoperative visual analogue scale (VAS), postoperative VAS, and VAS score changes among these three groups was noted. In the morbidly obese group, the postop Knee Society Scores, functional KSS, and Oxford Knee Scores were significantly poorer by 75.2, 70.5 and 33.1, respectively. Moreover, in the morbidly obese group, the amount of range of motion variations was significantly poorer. In 10 patients, complications like eminence fractures, insert dislocations, tibial component collapses and superficial infections developed. Six of them were morbidly obese, and four of them were obese. Besides, 11 of the patients needed revision. Eight of the patients were morbidly obese, and three of them were obese. Therefore, for functional outcomes and implant survival following UKA, it was concluded that morbid obesity is an independent risk factor. Nonetheless, with good planning and correct surgical technique, it is possible to get excellent results for obese and overweight patients. Morbid obese patients should be preoperatively talked about poor functional outcomes and high complication rates. Treatment of morbid obesity prior to the UKA surgery may be a good choice.