Objectives: Long work hours and overwork may increase the cardiovascular load of workers. But long work hours and overwork are not the same. Cardiovascular overload from working is dependent on the physical demand of the work and the worker's physical fitness, as well as the working hours. This cross-sectional study was designed to identify the association between overwork and cerebrocardiovascular disease, taking into account the physical demand of work, physical fitness, and work hours. Methods: Study data were obtained from surveillance of occupational cerebrocardiovascular disease. Questionnaire surveys including general and work-related characteristics were conducted. Maximum acceptable work time was estimated using the physical work demand and physical fitness of the subjects. The overwork index, which was the ratio of maximum acceptable work time and actual work hours of the subjects, was calculated. Results: In the workers with a moderate or high physical demand of work, the adjusted odds ratios for overwork indexes of 1.01–1.20, 1.21–1.50, and >1.50 were 2.679 (95% confidence interval (CI) 1.025–6.999), 3.124 (95% CI 1.111–8.783), and 4.331 (95% CI 1.719–10.908), respectively. Conclusions: The results indicate that the risk of cerebrocardiovascular disease might be high in the workers with long working hours, high physical demand of work, and poor physical fitness engaged in work with a moderate to high physical work demand. Work hours should be accommodated according to the worker's physical fitness and the physical demand of work, and this could lower the risk of cerebrocardiovascular disease.(J Occup Health 2015; 57: 51–57)