The purpose was to investigate risk factors for postoperative stiffness and long-term outcome following manipulation under anaesthesia (MUA). In one of the five Danish regions, all patients in a 4-year period who received MUA following total knee arthroplasty (N=36) were included in two case-control studies. Data on potential risk factors were extracted from the Danish Knee arthroplasty Register and from a postal questionnaire including long-term outcome measures regarding pain, function and quality of life (Oxford Knee Score and EQ-5D). Previous knee surgery and a high preoperative Knee Society Function Score were significant risk factors, whereas attending a preoperative information meeting was associated with a significantly decreased risk of postoperative stiffness requiring MUA (P<0.001). The long-term results following MUA (1-5 years) were equivalent to patients without postoperative stiffness.