Primary headaches are characterized by an high prevalence, especially among workers. This issue entails remarkable costs, both direct and indirect. For a great amount, the latter consist in the loss of work days for this disease and in a decrease of occupational efficiency among these patients. Moreover, workers suffering from headache could be at high risk for occupational injuries, due to a reduction in attention and to the possible onset of adverse drug effects of their therapies. Thus, primary headache should not be no longe overlooked as an important occupational disease. Among putative risks factors that could increase the rate of headache's onset in the occupational environment, shift work is of great interest. We studied 97 workers (93 males and 4 females) of a single, chemical plant located in Lombardy (Italy). Considering only male workers, the prevalence of primary headache was found to be significantly high among shift workers compared to workers occupied only during the day (40.4% vs. 21.9%, p=0.043). Our results, although observed on a little population, seem to add some evidence, suggesting a role for shift work to increase the prevalence of headache among workers.