Objective The aim of the study was to examine patients' beliefs about having familial adenomatous polyposis (FAP), a hereditary colorectal cancer syndrome, and how these beliefs are associated with adherence to endoscopic surveillance. Methods Adult patients diagnosed with FAP on the national Swedish polyposis register who had undergone prophylactic colorectal surgery (n 209, response rate 76%) completed the Illness Perception Questionnaire (IPQ). Logistic regression analysis was used to investigate the relationships between illness perceptions and adherence, when controlling for demographic and clinical factors. Results FAP was less distressing in men and those with fewer symptoms, reporting less serious consequences and more coherent understanding of FAP. Non‐adherence (14%) to surveillance was associated with being older, having undergone surgery less recently and no history of malignancy. Patients' beliefs about their FAP were able to explain unique variance in non‐adherence, in particular those who believed FAP was less distressing. Conclusions Patients who were non‐adherent to endoscopic surveillance had more positive perceptions about their FAP and, in particular, were less emotionally affected compared to those who adhered. As non‐adherence implies a greater risk of future malignancies, special efforts are required to effectively prevent cancer in all patients with FAP. Those who have lived with the condition for a long time, and are not troubled by gastrointestinal symptoms or worried about their FAP, may be in need of specific information and support. Further prospective research is required to examine emotional predictors and consequences of non‐adherence. Copyright © 2015 John Wiley & Sons, Ltd.