Izmit Bay and its coastal environment was strongly affected by the August 17th, 1999 Izmit Earthquake. The changes in the Bay ecosystem and its chemical oceanography have been studied in detail previously [Okay, O.S., Tolun, L, Telli-Karakoc, F., Tiifekci, V, Tufekci, H. And Morkop, E. 2001. Yzmit Bay ecosystem after Marmara earthquake and subsequent fire: The long-term data. Marine Pollution Bulletin 42, 361-369; Balkys, N. 2003. The effect of Marmara (Izmit) Earthquake on the chemical oceanography of Izmit Bay, Turkey. Marine Pollution Bulletin 46, 865-878.]. In this study surface sediments collected from the Izmit Bay before and after the earthquake have been analysed for total and individual (14 compounds) polycyclic aromatic hydrocarbons (PAH). Analyses have been performed by high performance liquid chromatography with fluorescence detection (HPLC/FD). Before the earthquake, total PAH concentrations in the Bay sediments ranged from 120 to 8900 ng/g while after the earthquake PAH concentrations varied between 240 and 11,400 ng/g. Molecular indices based on isomeric PAH ratios used to differentiate the pollution sources, clearly indicate the differences in molecular distribution of PAHs before and after the earthquake. Sediment data obtained before the earthquake shows that most of the contamination originated from high temperature pyrolytic inputs while after the earthquake it originated from petrogenic sources. This difference emphasises the environmental impact of uncontrolled discharges from petroleum industries after the earthquake. The LMW/HMW ratio (sum of the low molecular weight PAHs / the sum of higher molecular weight PAHs) predominance also changed after the earthquake as a result of the strong water movements. According to the characteristics of aromatic rings distributed in the bay sediments, the soluble parts of the total PAH were probably transferred to the water column after the earthquake as a result of resuspension process. The TEL/PEL (Threshold Effect Level / Probable Effect Level) analysis suggests that the Izmit Bay sediments were likely contaminated by acutely toxic PAH compounds. (c) 2006 Elsevier Ltd. All rights reserved.