['To analyse the frequency of mistakes in communication between the physician and the patient and their incidence in errors in self-administered drugs.', "We undertook a descriptive, cross-sectional study based on interviews with a random sample of patients older than 65 years who were polymedicated (five or more drugs) and had multiple comorbidities. Data were analysed about the patients' reports of what the physician said, medication mistakes by the patients and their consequences.", "Responses were provided by 382 patients. A medication error in the last year was reported by 287 patients (75%), and 16 patients (4%) reported four or more errors. Most cases concerned the dosage, a similar appearance of the medication or a lack of understanding of the physician's instructions. Very severe consequences occurred in 19 cases (5%). Multiple comorbidities (P = 0.006) and a greater number of treatments (P = 0.002) were associated with making mistakes. Frequent changes in prescription (P = 0.02), not considering the prescriptions of other physicians (P = 0.01), inconsistency in the messages (P = 0.01), being treated by various different physicians at the same time (P = 0.03), a feeling of not being listened to (P < 0.001) or loss of trust in the physician (P < 0.001) were associated with making medication mistakes."] Does physician patient communication failure facilitate medication errors in older polymedicated patients with multiple comorbidities?