In central Europe, the economic and symbolic status of blue-collar workers has considerably declined since the end of Communism. How visible were workers in official statistics and in sociological research under Communism and afterwards? Doworkers as a social category gain visibility in scientific research when they have specific conditions of existence and a strong collective identity? For different reasons in Poland and Czechoslovakia, it is hard to talk about a working class under Communism even though authorities grounded their legitimacy on this class. After 1989, workers became invisible in both official statistics and sociology. Owing to the adoption of the International standard classification of occupations (ISCO) in central Europe and the use that national institutes of statistics have made of it in their publications, the boundary of the worker category has blurred. Since 1989, sociologists have shown little interest in workers for reasons that are discussed. A few case studies (mostly by Western academics) are mentioned to draw attention to the ambiguity surrounding this social category in sociology. A comparison between the ISCO and the french scheme Professions et Catégories socioprofessionnelles (PCS) shows the interest (and difficulty) that sociologists have in constructing nomenclatures that satisfy both them and statistical offices.