We use monthly personnel records of a large German company for the years 1999-2005 to analyse the gender wage gap (GWG). The unconditional GWG is 15 per cent for blue-collar and 26 per cent for white-collar workers. Different returns to entry age explain a substantial part of the GWG as well as segregation of men and women in different hierarchical levels. The relative GWG increases with increasing tenure for blue-collar but declines for white-collar workers. Taking into account the different impact of general and firm-specific human capital on white-collar and blue-collar occupation, this is consistent with theories of statistical discrimination.