Breast milk samples and blood serum collected from primipara women in Sweden during the period 1996 to 2004 were analyzed with the aim to study levels of perfluorinated chemicals (PFCs) and the concentration ratio between milk and blood. A total of five perfluorinated chemicals (PFCs) were detected in breast milk, of which perfluorooctanesulfonate (PFOS) and perfluorohexanesulfonate (PFHxS) were found most frequently. In addition, perfluorooctanesulfonamide (PFOSA), perfluorononanoic acid (PFNA) and perfluorooctanoic acid (PFOA) were detected. The highest mean concentration in individual milk samples was obtained for PFOS (0.172 ng/mL) followed by PFHxS (0.068 ng/mL) and PFOSA (0.012 ng/mL). The quantification of PFOA was hampered in most of the samples due to a high procedural blank contamination. A total of eight PFCs were detected in the serum samples. Breast milk levels in this study were on average 113 times lower compared to serum levels for PFOS, 57 times lower for PFHxS and 23 times lower for PFOSA. There was a strong association between increasing serum concentration and increasing milk concentration for PFOS and PFHxS. During the period 1996-2004, the levels in pooled breast milk samples were relatively constant with a slightly decreasing trend for the pools collected in years 2003-2004. Analysis of breast milk, consecutive sampled over a period of several days, did not indicate a decrease in levels with progression of lactation.