Objective: 1) To determine gender differences regarding therapeutic adherence in patients with arterial hypertension and type 2 diabetes mellitus. 2) To detect differences in terms of age. 3) To determine existing relationships in patient compliance levels between Morisky-Green's test, Batalla's test and the pill count expressed as a percentage of compliance. Method: Descriptive, transversal study, carried out for a period of 7 months in the Primary Health Care, Health Centre in Renteria-Beraun (Guipuzcoa), Basque Health Service (Osakidetza), with an incidental sample of 100 patients diagnosed with hypertension and type 2 diabetes mellitus and receiving oral treatment. Principal variables: age, gender. Conditioning variables: years of evolution of each pathology, number of prescribed medicines, time lapse of prescription collection, Morisky-Green's test, Batalla's test and pill count. Results: The statistical analysis yielded similar compliance for men and women, and for different age groups (Morisky-Green and pill count). Approximately 50% of the patients had adequate compliance according to at least one of the 3 tests. A greater relationship was found between Morisky-Green's test and the pill count method, and medication adherence improved when knowledge of the disease increased, and when the number of prescribed pills became smaller. Conclusions: Adherence varies according to the evaluation tool used, non-adherence is high and knowledge of the disease helps compliance. This suggests the convenience of systematically reviewing treatments and supplying more information to patients. (C) 2011 SECA. Published by Elsevier Espana, S.L. All rights reserved.