Abstract Muscle tissue of flatfish (dab, sole, flounder and plaice) from the Mersey Estuary and inner Liverpool Bay contain concentrations of ΣPCB(ICES 6) that range from 7.7–43.4 μg kg −1. Using a derived conversion factor of 3.0 for ΣPCB (ICES 6) to ΣPCB(A1254), concentrations of ΣPCB(A1254) in flatfish from the Mersey Estuary and Liverpool Bay range from 23–130 μg kg −1, the latter of which classifies into the ‘upper’ category of contamination as defined by the Joint Monitoring Programme of the Oslo and Paris Commissions. Values of ΣPCB(A1254) in Mersey Estuary flatfish are 1.2–4× higher than data reported for outer Liverpool Bay and the Irish Sea over the last twenty years. ΣPCBs in roundfish (cod, whiting) from the Mersey Estuary are low, though higher than in Liverpool Bay by a factor of up to 3×. Congeners No. 138 and No. 153 contribute much of the ΣPCB in all flatfish, with No. 180 and No. 101 present in significant but lesser amounts. The lighter, less chlorinated congeners No. 28 and No. 52, are absent from roundfish except those from the inner estuary. ΣPCBs in Mersey Estuary fish are 20–200 times higher than for the north-west Atlantic Ocean and the Solway Firth. For some Mersey Estuary fish ΣPCB values exceed national proscriptive limits set by the Environmental Protection Agency for the USA. Caution is advocated regarding the consumption of fish from industrialised estuaries, including the Mersey, though there are no statutory limits for PCBs in fish or fishery products within the European Union.