Objective: to study the association between musculoskeletal disorders in distal upper extremities (MSDUE) and the variable sex in the plastic industry. Method: cross-sectional study with 577 workers. The MSDUE was defined by the presence of pain in the previous twelve months, lasting for more than one week or having a monthly frequency, causing work restrictions or search for medical care, or severity ≥ 3 (from 0 to 5), in at least one of these regions: fingers, wrists, hands, forearms or elbows. Covariates of interest were: physical and psychosocial demands at work, sociodemographic and lifestyle-related variables, physical fitness and household work. Multiple logistic regression was used in order to investigate statistical interaction and presence of confounding variables. Results: MSDUE occurrence was higher among women, independently of the tested work-related and outside of work demands. Physical fitness was the interaction variable, and psychosocial demands was the confounding variable. Men who referred good physical fitness presented lower prevalence compared with those with poor physical fitness. Among women, good physical fitness was not enough to significantly reduce their high musculoskeletal morbidity. Conclusion: differences in workrelated exposure do not explain the higher morbidity among women. It is necessary to consider sex differences, either socially determined or related to biomechanics, resulting in distinct responses to work demands.