This cross-sectional study of a group of assembly workers (n=289) tested the hypothesis that affective stress responses mediate the effect of psychosocial work conditions on musculoskeletal complaints (MSCs). Self-reported work demands, control, social support, stress, energy, and MSCs were analysed in hierarchical logistic regression analyses. High work demands were related to a higher risk of shoulder problems. Work demands and social support, but not control, were related to stress; and more musculoskeletal complaints were found in the group with high stress than in the low-stress group. The analyses supported the hypothesis that the effects of work demands on shoulder problems were mediated by the affective stress response, whereas this did not seem to be the case for the effect of social support and control conditions on neck problems. A weaker relation to psychosocial work conditions was shown for back problems than for shoulder and neck problems. Relevance to industry: Psychosocial work conditions have repeatedly been shown to be related to risk of musculoskeletal complaints. Individual subjective stress responses may help to identify those who are at risk with respect to shoulder complaints.