Objectives Adjuvant endocrine therapy for early-stage breast cancer has greatly reduced the morbidity and mortality associated with breast cancer recurrence. Despite this, a significant proportion of women report fears of cancer recurrence. This study examined the associations between fear of cancer recurrence (FoR) and illness perceptions, medication beliefs, and treatment side effects in women taking adjuvant endocrine therapy following breast cancer. Methods A total of 153 post-menopausal women with early-stage breast cancer completed a postal survey. Analyses were conducted to examine the association between FoR and illness perceptions, medication beliefs, treatment side effects, demographic factors, and emotional distress and to identify which of these factors would be most strongly associated with FoR in a regression model. Results All illness perceptions (apart from personal control) were associated with FoR, as were patient beliefs about endocrine therapy. Although treatment side effects, being unemployed, and higher levels of anxiety and depression were associated with FoR, only illness perceptions (identity, treatment control, timeline, and emotional representation) and medication necessity beliefs were significantly correlated with FoR in the final model. Conclusions It appears that, in addition to directly targeting FoR, it may be worthwhile to address the illness and medication beliefs supporting the fear. Additionally, helping women to differentiate everyday symptoms from those indicative of breast cancer may help to reduce fear of recurrence.