Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) are important perfluorochemicals (PFCs) in various applications. Recently, it has been shown that these chemicals are widespread in the environment, wildlife and humans. But the kinds of factors that affect their levels in serum are unclear, and it is also not clear whether exposure to them is increasing or not. To investigate the impacts of time, geographical location and sex on the levels of these chemicals, we measured PFOS and PFOA concentrations in human sera samples collected both historically and recently in Miyagi, Akita and Kyoto Prefectures in Japan. The PFOS and PFOA levels in sera [Geometric Mean (Geometric Standard Deviation)] (microg/L) in 2003 ranged from 3.5 (2.9) in Miyagi to 28.1 (1.5) in Kyoto for PFOS and from 2.8 (1.5) to 12.4 (1.4) for PFOA. Historical samples collected from females demonstrated that PFOS and PFOA concentrations have increased by factors of 3 and 14, respectively, over the past 25 yr. There are large sex differences in PFOS and PFOA concentrations in serum at all locations. Furthermore, there are predominant regional differences for both PFOS and PFOA concentrations. In Kyoto the concentrations of PFOA in dwellers who had lived in the Kinki area for more than 2 yr were significantly higher than in people who had recently moved into the area, in both sexes. This finding suggests that there are sources of PFOA in the Kinki area that have raised the PFOA serum levels of its inhabitants. Further studies are needed to elucidate these sources in the Kinki area of Japan.