We measured concentrations of aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), total mercury (THg), methylmercury (MeHg), selenium (Se), silver (Ag), and zinc (Zn) in liver from Harbor Seals (n  =  31) stranded dead in the inland waters of Washington State between 2004 and 2007. Results were compared by age class and region, and to results from past studies. Significant differences in concentration were detected among age classes, regions, and years. Adult seals (>3 y old) from this study had significantly higher concentrations of As, Cd, THg, MeHg, Ni, Se, and Ag than neonate pups. Seals from the eastern Strait of Juan de Fuca (SJF) had significantly higher concentrations of As, MeHg, Se, and Ag than seals from the southern Puget Sound (SPS). When pooled with past studies, significant age and regional differences were detected for Zn and Cu, respectively, where Zn decreased with age and Cu was higher in SJF than SPS seals. Lead was significantly lower in seals from the present study compared to past studies. Examining the concentrations of both essential and non-essential trace elements indicates that Harbor Seal tissues can be useful in detecting regional and temporal trends in contaminants.