Objective:  The present study sought to assess whether any statistically significant differences exist between evaluations conducted by medical doctors and those by social workers within the National Social Security Institute (INSS), regarding identification of disability using the adapted Brazilian functionality index to grant retirement. Method To do this, an analytical investigation was done using the official INSS database for the period from October 2013 to January 2016, regarding evaluations to confirm disability among workers who were insured through the INSS. The analysis was conducted using the R software, version 3.4.1. A concordance index, significance analysis and the Pearson correlation test were applied. The sensitivity and specificity of the evaluations made by doctors, by social workers and by both were calculated. Arating index was obtained by dividing the result from the doctors’ evaluations by the result from the social workers’ evaluations. Results The correlation analysis using the R software showed that there was no statistical difference between the evaluations conducted by medical doctors and social workers. However, differences were observed in relation to calculation of the sensitivity of the evaluations, and in the analyses on the rating index and standard deviation between the doctors’ and social workers’ evaluations, especially in the domains of sensory function, domestic life and education, work and economic life. Conclusions This study demonstrated that there is a difference between evaluations conducted by medical experts and by social workers, which can be explained in terms of each professional’s interpretation of what is defined in the manual. The criteria used to define the rules for obtaining the benefit should be discussed. We highlight that the prerequisite for identifying a disability is that an impairment should be characterized by means of the International Classification of Diseases (ICD-10), which is a medical prerogative.