This paper presents survey results on the size and structure of the hidden labour market in The Netherlands. According to the results total income from hidden work is at least 1 percent of national income. The hidden income is shared by more than one million participants (nearly 12 percent of the corresponding population). This result is lower than various other estimates of the magnitude of the hidden economy. Some definitional and methodological issues are discussed in order to explain the difference from the other estimates.The most notable results of the survey refer to the structure of the hidden labour market. At one end of this market are people with a high wage rate, working relatively few hours. They have the characteristics which given them a favourable position in the formal labour market. At the other end are people with low hidden wages, who work more hours. They have difficulty in finding a formal job. The income from hidden labour is distributed in very much the same way as income from formal activities. There is no evidence that the hidden labour market compensates those who are worse off in the formal economy.