In January and February 1990 a mass-stranding of Razorbills and Guillemots was recorded in the Netherlands. Densities on the mainland coast were unprecedented (figure 1). Most birds were heavily oil contaminated and the stranding was accompanied by an oil stranding in Noord-Holland. The extremely turbulent weather made a final assessment of numbers beached very difficult. Most corpses disappeared in one or two days time, many counts were therefore unreliable and hence, the actual density is probably at least twice as high as it was recorded in the Systematic Survey (cf. Camphuysen 1989a). Razorbills, although found in slightly smaller numbers than Guillemots, were more abundant than ever before. All age groups were represented, with slightly more first year birds than usual. Few first-year Guillemots were reported; adults (or older immatures) predominated and many birds were already in summer plumage. Very few bridled morphs were found. Besides Razorbills and Guillemots also the number of Puffins was rather large. Hardly any other bird was found on the coast: 90% of all corpses were either Razorbill, or Guillemot. A further analysis of the event, when all relevant data are received, will be prepared later.