Introduction Mental health status is related to work context and content. There are many stressful conditions at work associated to negative effects on workers’ health. According to the World Health Organisation (WHO), common mental disorders affect more than 30% of employed workers. Mental and behavioural disorders are the third main cause of social security benefits payment in Brazil. This study aims to raise the prevalence of mental illness among employees of two metallurgical companies and differences between them.

Methods A descriptive cross-sectional study was carried out in two companies located in São Paulo State, Brazil, in 2016. Participants were 440 workers – 146 from company A and 294 from company B. They answered a sociodemographic questionnaire and the WHO´s Self-Report Questionnaire with 20 questions about mental symptoms (SRQ-20). Cases were participants with seven or more positive answers in SRQ-20.

Results Company A produces wires for the construction industry and B is a metallurgical producer of steel cables for the oil and mining industry. The prevalence of mental illness among the participants was 15.17% (company A) and 12.28% (company B). There was a higher percentage of mental symptoms among company A women (66%) than company B´ (26.6%). About education, participants with more than 12 school years presented more mental illness in company B (36.8%) than company A (19.5%). In general, ‘to feel nervous, tense, worried’, and ‘sleep badly’ were most common positive answers in both groups.

Discussion Mental illness prevalence was similar among both groups and results were similar to other studies. Company A women and Company B high education workers would be at higher risk for mental problems. It´s necessary to provide medical and psychological support to cases and preventive actions should be offered to promoting health among employees of those companies.