During spring and autumn, ILVO-DVI carries out sea-going surveys for environmental monitoring purposes. Fish disease quantification is an integral part of biological and chemical monitoring. The aim of the present study was to monitor if higher prevalence of diseases and parasites could be detected on dredge spoil disposal sites on the Belgian Continental Shelf (BCS) in the period 2004-2005. Therefore, an important number of infectious and parasitical anomalies of the epidermis, the gills and the mouth of several fish species are recorded since 1995. Severe diseases such as skin ulcers, nodules, skeletal malformations and lymphocystis, which can indicate effects of pollution, are rare on the investigated zones of the BCS. No significant differences could be detected between the dumping sites and the reference zones. Most of the observed anomalies were due to parasites, which show considerable variation in spatial and temporal distribution, and could not be related to a specific zone.