Why do workers change occupations? This paper investigates occupational mobility and its determinants following a large unexpected shock (communism's collapse in 1989.) Our calculations show that from 1989 to 1995 between 35 and 50 percent of Estonian workers changed occupations (classified at one- and four-digits, respectively). Among the main determinants of occupational mobility we find firm tenure, labour market experience and returns to alternative occupations. We investigate the role of gender and ethnicity and find strong results for the former, with mobility mainly driven by push factors for males (returns to current occupations) and by pull factors for females (returns to alternative occupations).