The article deals with the notion of purity and its relation to Good Citizenship and the development of Roma policies in Sweden during the twentieth century. The case of the differentiation between "zigenare" and "tattare" is presented as an example of how ideas about purity informed processes of categorization, inclusion, and exclusion during the formative and expansive years of the Swedish welfare state. The medical sciences had a dominant role in these processes. Examining and defining "pure zigenare" was one of the ways in which experts would differentiate between legitimate and illegitimate Romanies– or Tolerated and Failed Citizens–in the post-war period. These differentiations had real and lasting consequences as they worked to support certain Romani groups while ignoring others, all of which are today included in the Swedish national Roma minority.