The incidence of obesity, defined as the fraction of persons with BMIs exceeding 30·0, was examined in two birth cohorts of 40–50-year-old occupationally active inhabitants of the city of Wrocław, Poland. In both cohorts and both genders obesity increased monotonically with decreasing position on a three-level educational scale. During the 1986–1996 decade obesity increased dramatically among males with trade school education only; concomitant shifts were much smaller or absent in the college-educated groups. The contrast in obesity between the opposite ends of the educational scale has widened markedly in both genders; and the between-gender gap has declined somewhat.