Temporal trends of polyfluoroalkyl compounds (PFCs) were examined in liver samples from harbor seals (Phoca vitulina) collected from the German Bight (1999-2008). Concentrations of various PFCs, including C ₄-C ₁₀ perfluoroalkyl sulfonates (PFSAs), perfluorooctane sulfinate (PFOSi), perfluorooctane sulfonamide (FOSA) and C ₈-C ₁₅ perfluoroalkyl carboxylic acids (PFCAs) were quantified. Perfluorooctane sulfonate (PFOS) was the predominant compound with a maximum concentration of 3676 ng g ^-1 ww (1996), making up on average 94% of the measured PFCs. Significantly higher concentrations were found in <7 month old in comparison to ≥7 month old harbor seals for C ₆-C ₈ PFSAs, perfluorododecanoic acid (PFDoDA) and FOSA, whereas perfluorodecanoic acid (PFDA) showed significantly lower concentrations in the younger harbor seals (p < 0.05). These results suggest a transplacental transfer of PFCs to the foetus and/or consumption of different contaminated food. Regression analysis of logarithmic transformed PFC mean concentrations indicated a significant temporal trend with decreasing concentrations for C ₅-C ₇ PFSAs (p < 0.001), PFOSi (p = 0.028), FOSA (p < 0.001) and perfluorooctanoic acid (PFOA) (p = 0.031) between 1999 and 2008. Furthermore, PFOS decreased by 49% between 1999 and 2008, which correspond with decreasing concentration levels of its metabolic precursors PFOSi and FOSA of 83% and 95% in the same time period. However, the decreasing trend of PFOS is not significant (p = 0.067). The reason for the decline during the past 10 years could be an effect of the replacement of these PFCs by shorter chained and less bioaccumulative compounds. But the observations of increasing perfluorodecane sulfonate (PFDS) levels (p = 0.070), the high concentrations of PFOS and constant levels of C ₉-C ₁₃ PFCAs indicates that further work on the reduction of environmental emissions of PFCs are necessary.