To investigate the relationship between precarious working conditions and the health of bus drivers and conductors.Data were gathered by means of a survey and interviews conducted in 2012 with 1607 employees of the public transport system of the metropolitan region of Belo Horizonte, Brazil. Nine proxy variables were used to create a precariousness score, ranging from 0 to 9, on a comparative scale: score 0 "less precarious" and 9 "more precarious." Negative self-evaluations of health, medical diagnoses of depression and sleep disorders, common mental disorders, musculoskeletal pain and medical leave were assessed. Poisson regression was used to assess associations between precariousness and health adjusted for age, sex, education, vibration, and noise.The sample was composed of 853 drivers and 754 conductors. Most were men (87%), with age below 40 years (67.4%) and medium educational level (64.5%). The maximum precariousness score observed was 7. Most individuals were in the groups of scores 3 (26.7%) and 4 (26.1%). The prevalences of the health situations were: common mental disorders, 26.3%; medical diagnosis of depression, 9.7%; medical diagnosis of sleep disorder, 14.6%; musculoskeletal pain, 43.0%; medical leave (absenteeism), 34.8%; and negative self-evaluation of health, 20.2%. The prevalences of health conditions, with the exception of negative self-evaluations of health, were significantly higher among workers with higher levels of precarious working conditions.Worse health, particularly common mental disorders, was associated with self-assessed work precariousness.