OBJECTIVE : To design a questionnaire to identify patients with difficulties to obtain, understand and use health information. METHODS : Qualitative study through semi-structured interviews and a consensus technique. A review of the literature on health literacy was carried out. Five semi-structured interviews were conducted with experts in the field. A 12-item instrument was designed. Content validity was determined using the Health Consensus technique. Participants were health professionals and patient representatives (5 semi-structured interviews and 60 Health Consensus). An instrument to measure the level of skills and literacy in patients' health was developed. The measures were 7categories on the health competencies and literacy construct: Ability to search for information, ability to understand the information, ability to communicate with health professionals, capacity for operational understanding, competence in decision making, ability to move and navigate through the health system, and competencies in self-care. RESULTS : A 12-item questionnaire was designed. The median scores obtained in the Health Consensus ranged between 6.08 (1.43) and 7.22 (1.52), with an agreement level of between 73.87% to 84.19%. Finally, a 5-item instrument was obtained to assess the patients' health competencies. CONCLUSIONS : The questionnaire is a useful tool to detect those at risk of having difficulties in obtaining, understanding and using health information. This would allow professionals to focus their attention on the type of information patients need and better adapt it to their needs.