During WWII, the Nazis exterminated most Czech Gypsies. Most Czech Gypsies of today were moved there (most of them forcibly, and often on the place of deported Sudeten Germans) from Slovakia. Many of them lived in workers' housings at factories, which later didn't count as permanent residence, or in special settlements where they weren't registered. Children given to foster parents or foster homes were without permanent residence permits, too.
After the break-up of Czechoslovakia, the new citizenship law was designed (consciously, see in this article) to disenfranchise Gypsies (and prevent further immigration from Slovakia) by exploiting the previous circumstances and more, all the while speaking about "Slovakians". Applicants had to have proof of residence, the five-year crime-free record, and renouncement of Slovakian citizenship (which many of them didn't have in the first place, having been born to "Slovakian" Gypsy parents in the Czech Republic).
Worsening the problem were practical issues like the legal inexperience and lack of counsel of most Gypsies, and local courts who interpreted laws their own even worse way (a worst example: one "Slovakian" Czech Gypsy was forced to go to Slovakia to bear her child; but also examples of rewoking citizenship).
As a result of these combined reasons, in 1993, about 100,000, that is half of Czech Gypsies became stateless.
Now this was not the end of the story. Major amendments were forced on the law: in 1996, by when about 20,000 stateless Czech Gypsies remained, the crazy 5-year-no-crime-record rule (which was valid irrespective of seriousness of the crime - stealing a bread four years ago was a valid reason for exclusion, being sentenced for murder six years ago was not) was eased to a case-by-case basis. In 2000, by when about 10,000 stateless Roma remained thanks to increased NGO activity, the law was finally changed big-time by allowing declaration of pre-1991 residence. Only those who moved away since or sought asylum elsewhere remain excluded. *Traitor*, n. A benighted individual who perceives an illusory distinction between serving his nation and abetting the criminals who govern it.
As explained, almost none were "left" in the Czech Republic after 2000. However, many of those excluded because they moved into other countries in the meantime (most of them to Slovakia) moved back. For those moving away, I found figures of 20,000-25,000, or 10% of the total; for total Roma immigrants from Slovakia (Czech Romas moving back + Slovakian Romas newly moving) I saw similar numbers. What I'm not clear about and would have to look up (as can also be seen from the termination of my account in 2000) is whether further changes have been made to the law around the time of the Czech Republic's joining of the EU.
BTW, last time I forgot to note two further nasty hurdles in the original law designed to hit poor Gypsies: the hefty legal prices involved ($300 per person) and the requirement of dual parental approval for children's applications (hitting both children of divorced and children in orphanages). *Traitor*, n. A benighted individual who perceives an illusory distinction between serving his nation and abetting the criminals who govern it.