While there is a growing body of evidence that informal payments for health care are widespread and enduring in the former communist countries of Central and Eastern Europe and Central Asia, evidence on the scale of the phenomenon is not only limited, but what is available is often conflicting. Hungary exemplifies this controversy, as the available literature provides conflicting figures, differing by an order of magnitude among various surveys, with a similarly large difference between survey findings and expert estimates. This study advances understanding of the methodological issues involved in researching informal payments by providing a systematic analysis of the methodology of available empirical research and official statistics on the scale of informal payments in Hungary. The paper explores the potential sources of differences, to assess the scope to reduce the differences between various estimates and to define the upper and lower boundaries within which the true magnitude of informal payments can be expected to lie. Our analysis suggests that in 2001 the overall magnitude of informal payments lay between 16.2 and 50.9 billion HUF (euro 64.8- euro 203.6 million, US dollars 77.1-242.4 million), which amounted to 1.5-4.6% of total health expenditures in Hungary. Looked at this way, informal payments do not seem to be an important source of health care financing. However, as informal payments are unequally distributed among health workers, with the bulk of the money going to physicians, with some not taking any informal payments, family doctors and some specialists may have earned between 60 and 236% of their net official income from this source in 2001. This suggests that it is not the overall amount of informal payment that makes it a policy concern, but the consequences of its unequal distribution among health workers. What is remarkable about informal payments in Hungary is that a relatively small amount of money can keep the system running, which gives rise to the hypothesis that, in certain cases, it is the hope of substantial informal payments in the future that motivates physicians to remain in the system. This is a difficult challenge for policy-makers as it would require a much larger amount of money to achieve equilibrium under any formal alternative.