We examined the prevalence of fatigue and its association with occupational conditions and health-related habits in 3785 industrial employees of six industrial sectors to define modifiable factors. The factors examined included complaints of fatigue during and after work, an ergonomic evaluation of employees' workstations, demographic characteristics, and health-related habits. Eighteen percent of the subjects complained of severe fatigue frequently or very frequently. We were able to identify two major modifiable variables that were independently associated with the presence of fatigue. Logistic regression showed that those workers who did not participate in physical activity at least once a week had a 1.7-fold increase in prevalence of severe fatigue (95% confidence interval = 1.3 to 2.3, P < 0.001). The other major modifiable factor was temperature control, with those workers who worked at non-temperature-controlled workstations having a 50% increase in the prevalence of fatigue (odds ratio = 1.5, 95% CI = 1.1 to 2.1; P = 0.01). Accidents were significantly more frequent in those workers with fatigue. Further studies should focus on intervention programs to modify the factors identified by this study.