The objective of this work was to validate the content of a scale formulated in Spanish for older adults in Mexico, with the aim of comprehensively measuring the access of this population group to outpatient primary-care services. To this end, we carried out a methodological content-validity study in four stages: (1) construction of the scale; (2) evaluation of item legibility; (3) quantitative content evaluation by two groups of judges selected by convenience: participant-judges including older adults with adequate reading comprehension, surveyed in person (n = 23), and expert-judges comprised of researchers specialized in the fields of health services, psychometrics and aging, surveyed online (n = 7); and (4) collection of qualitative feedback from several of the participant-judges (older adults, n = 4). The content was validated both by sequentially examining the level of consensus in the responses of both groups of judges, using the Tastle and Wierman method, and by calculating Aiken’s Validity Coefficient with a 90% confidence interval. The scale contained 65 items pertaining to 10 dimensions of two major constructs: accessibility (n = 39) and personal abilities (n = 26). Five items were eliminated in accordance with the minimum-consensus criterion (0.5). This is the first psychometric scale to be developed in Mexico with the view of integrating the characteristics of health-care services and the abilities of the older adults in a single questionnaire designed to measure the access of this population group to outpatient primary-care services.