Joint replacements are effective surgical interventions, yet some patients report experiencing ongoing physical and psychological symptoms post-operatively. An important parameter of recovery is exercise rehabilitation, yet little is known about the role of adherence in patient outcomes. Guided by the Common Sense Model and the Social Cognitive Theory the aim of this thesis was: (a) to identify determinants of exercise adherence, physical and emotional outcomes (b) and to examine whether adherence mediates the relationships between determinants and outcomes. In order to address these objectives a longitudinal study was first conducted. Osteoarthritis patients undergoing total hip and knee replacements (T1, n=54) were assessed at pre-surgery and at six weeks and nine months after surgery (T3, n=40). As determinants of adherence are multifactorial, factors that influence exercise adherence were further explored from a patients’ (n=8), and physiotherapists’ (n=5) perspective in a qualitative study using focus groups. A systematic review indicated that post-operative self-efficacy is a more consistent predictor of outcomes compared to pre-operative self-efficacy. Before surgery, emotional health was related to negative emotional reactions and strong beliefs of general self-efficacy while pre-operative physical status was associated with higher perceived illness identity and general self-efficacy. In a time-frame from baseline to nine months following surgery physical outcomes improved, exercise adherence decreased, emotional health remained stable while changes in patients’ cognitions and emotions were variable. Subsequently, changes in cognitions and emotions influenced post-operative outcomes. Early decrease in general self-efficacy and increase in consequences predicted early emotional outcomes while late changes in emotional representations and general self-efficacy predicted late emotional indicators. Early increase in chronic timeline perceptions and decrease in challenge emotion predicted early adherence while decrease in early personal control predicted lower late adherence. Increase in perceived consequences was the most consistent predictor of early functional outcomes whereas late increase in rehabilitation self-efficacy was the most consistent predictor of late physical outcomes. The mediation hypotheses were not confirmed. The qualitative study indicated a number of factors relating to the health care system-, health care professional- and patient level that may contribute to patients’ exercise adherence. The findings of the series of studies presented have implications in terms of the content and the implementation timing of future interventions aiming to optimize outcomes in this group of patients.