Hungary's hidden economy is worth around €22 billion, accounting for 24% of gross domestic product compared to the European average of 20%, according to a report by Visa Europe.
The company said on Wednesday that two thirds of the value of the hidden economy is unregistered labour, while the remaining third arises from tax evasion.
The sectors especially hit by the shadow economy are construction, retail, manufacturing, tourism, personal services and farming.
The company attributed Hungary's relatively large hidden economy to "a lack of confidence in government and a complicated tax system".
Switzerland and Austria have the smallest black economies, at 8% of annual GDP.