Financial literacy is a path to sustainability and has an important role in ensuring the financial sustainability of individuals, families, enterprises and national economies. The level of these economic indicators such as debt, payment discipline, savings and financial management all translate into prosperity or insolvency and bankruptcy and result partially from financial literacy. The higher the level of financial literacy, especially of young people, the more favourable the level of economic indicators, which translates into the economy and sustainable development. With this study we aim to determine the level of financial literacy of high school students in Poland and to determine whether financial literacy changes according to gender. The most important element that distinguishes our study from the others is that or study was carried out with a large sample of high school students with an average age of 15−16 years. In addition, the effect of gender on financial literacy at an early age was investigated, also comparing the wider themes to the so-called narrow themes. The results of the research demonstrated a good and partially very good, level of financial knowledge of the young people in Poland. 45.3% obtained an average level score and 43.8% achieved a high-level score in financial knowledge. This result shows that they can be rational in their financial decision making. However although, it is understood that gender makes a difference on financial behaviour and use of financial instruments, gender does not make any difference on the level of financial knowledge. Moreover, the financial literacy level of males is found to be higher than females.