The sample estimates are uniformly below those of the Financial Accounts, even after harmonising all the definitions and the evaluation criteria. Such a problem can stem from the interviewee’s unwillingness to disclose the actual value of the asset (under-reporting). The paper presents a method to correct this potential source of bias in order to improve Survey of Household Income and Wealth financial assets. We use a sample survey of customers of the Unicredit group, coupled with administrative data on the assets actually owned, as external sources of information. The adjustment procedure enables to account for a large share of the gap between the figures derived from the sample and from the Financial accounts, significantly increasing the average value of the financial assets (inflating the unadjusted figure of 22.000 euros to 59.000 euros, amounting to about 85 percent of the Financial account estimates). The adjustment produces a larger correction for private bonds and mutual funds. The intensity of the correction is higher for one-person households, when the head of household is less educated or not employed, and it raises with his/her age.