The purpose of this study was to develop the Health and Work Survey (INSAT) and examine the validity of the discomfort rating scale. Data were collected from 706 Portuguese workers from six economic sectors with the support of the Health and Work Survey (INSAT-Inquerito Saude e Trabalho). The INSAT is a self-administered questionnaire to assessing working conditions, health and wellbeing, and to provide information to the occupational health systems in the organisations. For the survey instrument validation, the Rasch Partial Credit Model (PCM) was used to analyse item fit statistics. From the application of PCM, Person Separation Reliability was obtained (0.8761) and the value can be considered very good (>0.8). From the statistical analysis, the Overall Model fit information, given by Outfit Mean square/Infit Mean square, is between 0.5 and 1.5, meaning "Productive for measurement" and "acceptable fit overall". The INSAT items can generate predictable response patterns. We recommend that the INSAT discomfort rating scale and some other items should be reviewed in future works. In any event, this tool proves to be useful in assessing the relationship between work and health and in evaluating key main risk factors, helping to prevent problems and improving occupational health systems.