The number of offshore wind farms in Europe and elsewhere has substantially in creased in recent years. This rapid development has raised concerns about potential impacts on marine wildlife, particularly on seabirds, as these can be negatively affected through collision and displacement. While collision risk has been the focus of a number of studies, information about displacement of seabirds is scarce. Here we present data from an extensive survey program that aimed at determining the effects on seabirds of the first German offshore wind farm, 'alpha ventus'. Data were collected by line transect surveys during the first 3 yr of operation. We found significant displacement of 5 species with 75-92% lower abundance inside compared to outside the wind farm. For 3 species, the response distance to the outermost turbines was estimated to exceed 1 km. Two gull species were attracted to the wind farm site. Our results and a review of the available literature revealed good agreement with respect to the sign of the response (avoidance vs. attraction) but considerable differences in the strength of the response and the spatial extent of the disturbance outside the footprint of wind farms. While it seems unlikely that small-scale displacement by single wind farms would have an impact at the population level, the extent of the proposed development of offshore wind energy warrants further research into cumulative effects and their biological significance for seabird populations.