Considering the foregoing, the present study aims to evaluate the work ability index in Portuguese workers in various professions and see how the ability to work is linked to demographic characteristics. A cross-sectional study was carried out, including 1955 workers (40,3% males) from chemical and metal-mechanic industry, nurses, teachers and public administration. Subjects responded to self-administered questionnaires evaluating demographic characteristics and work ability index. The causal relationship between the sociodemographic characteristics and the WAI was quantified by calculating the odds ratio and confidence intervals of 95%.