OBJECTIVE: To examine the relation between illness cognitions and two measures of adherence in patients with hypercholesterolaemia, a disease marked by chronically high cholesterol. DESIGN: Cross-sectional. Based on the self-regulation model (Leventhal, Diefenbach, & Leventhal, 1992), patients' illness cognitions were predicted to be related to cholesterol control and medication adherence. Patients with illness cognitions consonant with an experts' mental model of hypercholesterolaemia were expected to show better control and adherence. METHOD: Hypercholesterolaemic patients (N = 169) were recruited at a university-based general medicine clinic. Patients completed a survey that assessed beliefs about hypercholesterolaemia and medication-taking behaviour. Cholesterol levels were obtained from patients' medical charts. RESULTS: Low-density lipoprotein (LDL) cholesterol control was related to believing that hypercholesterolaemia is a stable, asymptomatic disease with severe coronary consequences, and self-report of medication adherence was related to believing that the disease has severe coronary consequences (ps <.05). LDL cholesterol differences between groups low and high in various illness beliefs ranged between 0.04 and 0.24 mmol/l (2 and 9 mg/dl) which translated to between 1% and 18% lower LDL cholesterol levels. CONCLUSION: The present study shows several relations that have not been previously demonstrated between better LDL cholesterol control and illness cognition, cognitions that were similar to an expert or physician's mental model of hypercholesterolaemia. The magnitude of differences in patient cholesterol levels was small but may be clinically important.