Background Total knee arthroplasty is a common procedure with generally good results. However, there are still patients who are discontented without known explanation. Contentment and discontentment have previously been captured by quantitative designs, but there is a lack of qualitative studies regarding these patients’ experiences. Qualitative knowledge might be useful in creating strategies to decrease the discontentment rate. Methods Of the 348 patients who responded to a letter asking if they were contented or discontented with their surgery, 61 (18%) reported discontentment. After excluding patients with documented complications and those who declined to participate, semi-structured interviews were conducted with 44 patients. The interviews were analyzed according to qualitative content analysis. The purpose was to describe patients’ experiences of discontentment one year after total knee arthroplasty. Results The patients experienced unfulfilled expectations and needs regarding unresolved and new problems, limited independence, and need for buttresses. They were bothered by pain and stiffness, and worried that changes were complications as a result of surgery. They described inability to perform daily activities and valued activities. They also felt a need for buttresses, and a lack of respect and continuity, support from health care, and information adapted to their needs. Conclusion Patient expectation seems to be the major contributing factor in patient discontentment after knee replacement surgery. This qualitative study sheds light on the meaning of unfulfilled expectations, in contrast to previous quantitative studies. The elements of unfulfilled expectations need to be dealt with both on the individual staff level and on the organizational level. For instance, increased continuity of healthcare staff and facilities may help to improve patient contentment after surgery.