About 15-20% of the employees in Europe and in the USA are engaged in shift work that involves night work. Some experimental and observational data indicate that this type of work might lead to circadian disruption, including disruption in the melatonin synthesis - a hormone of anticarcinogenic and antioxidative properties. A hypothesis that there is a potential link between exposure to light at night and the risk of breast cancer was formulated for the first time by Stevens in 1987. Since then, relatively few epidemiological studies have been carried out in this area (15 studies including 8 cohort and 7 case-control studies). All of them are reviewed in this article. The majority of the epidemiological studies performed to date have focused on the association between shift work and breast cancer risk, few studies have reported an increased risk of other cancers, including colorectal cancer, endometrial cancer, prostate cancer and non-Hodgkin's lymphoma. In six out of ten studies, a statistically significant association between night shift work and risk of breast cancer has been shown (OR = 2.2; 95% CI: 1.1-4.5 in nurses in Norway with > 30 years of night shift work). The increased cancer risk has been reported in nurses, radio-telephone operators, flight attendants, and women employed in the enterprises, in which 60% of employees work at night. Most of the analyses have been based on the data from the registries, with limited potential for the exposure assessment and confounders adjustment. Although some epidemiological studies suggest an increased risk of breast cancer among nurses, we are still far from drawing final conclusions. Therefore, further epidemiological studies are warranted.