Since the early eighties, polychlorinated bifenyls (PCBs) and organochlor pesticides (OCPs) have been monitored in sediment of the Belgian Continental Shelf (BCS) by the laboratory of organic contaminants of the Sea Fisheries Department. PCBs and OCPs are both determinants of highest priority in the international monitoring programmes of OSPAR (North Sea Task Force, 1993). Sediment samples are annually taken at more than 10 sampling stations by a Van Veen grabber on board of the research vessel Belgica. Sediment samples are stored frozen prior to analysis. As organic contaminants tend to adsorb on the fine matter, the sediment fraction less than 63µm is isolated by wet sieving. After Soxhlet extraction of the dried fine sediment fraction and removal of inorganic sulphur, the sample is cleaned-up and fractionated on a deactivated aluminum oxide and a silica column, respectively. Finally, the two fractions are quantified by a GC-system equipped with an electron capture detector (ECD). As such, 10 PCB congeners (CB 28, 31, 52, 101, 105, 118, 138, 153, 156 and 180) and 9 organochlor pesticides (HCB, alfa-HCH, lindane, transnonachlor, dieldrin, endrin, p,p’-DDT, p,p’-DDD and p,p’-DDE) are analysed. The participation at international laboratory proficiency tests organized by QUASIMEME is an important part of the quality assurance programme. Contents of PCBs and OCPs are expressed as nanogram per gram of dry fine sediment. In order to assess the BCS, the values for 8 sampling stations were averaged and considered as representative. The sampling stations consisted of 4 dredge dumping sites (Zeebrugge S1, Zeebrugge S2, Zeebrugge Oost and Oostende) and 4 reference stations (Oostende Bank, Raan, Steendiep and Westdiep). Results obtained between 1991 and 2003 are discussed.Between 1991 and 2003, highest PCB and OCP values were observed in 1993. The sum of 10 PCBs amounted 30ng.g -1 , but gradually decreased to 9ng.g -1 in 1997. From then on, an increase up to 23ng.g -1 in 2002 was measured. In 2003, the PCB level dropped to ...