The aims of this study were (1) to investigate what are the illness perceptions of hypertensive patients and their relationship with beliefs about specific medicines, and (2) to identify different illness schemata and how they relate to the choice of medication. This was a cross-sectional study in which 191 Portuguese patients (59% females), with a hypertension diagnosis, aged over 18 years old, were recruited from a hospital clinic in the Lisbon Metropolitan area. The questionnaire included measures of choice of medication, beliefs about specific medicines (BMQ-Specific), illness perception (Brief-IPQ), and socio-demographic information. The results indicated that the components of the illness perceptions were associated with patients’ beliefs about necessity and concerns about medication. Patients seem to differ in their choice of medication (generic or brand names) according to the three illness schemata identified. Patients with more negative illness schemata were more likely to choose a brand medicine, whereas patients with a more positive perception of hypertension were more likely to choose a generic medicine. Our findings support the argument that illness perceptions and beliefs about medicines play a role in influencing patients’ preferences of medicines for the treatment of hypertension.