Computer science is a relatively new subject in schools and as such is not fully established. The way of conducting classes, as well as the content of computer science itself, changes with every new knowledge about the needs and difficulties that the students are faced with. Unfortunately, there is very little research related to the difficulties faced by high school students, and there is even lessresearch on students' difficulties in specific parts of the course material. It is precisely this lack of research that this thesis tries to modestly fill. This thesis presents the results of research conducted on 304 second-grade gymnasium students with the aim of discovering the difficulties students encounter when working with lists in the Python programming language. From the results of the test composed of 22 multiple-choice items, some students' difficulties were observed. The results of this research show that students have difficulties with understanding how lists are indexed, they showed difficulties with multiplying a list by an integer, and to a large extent, they have problems with using some of the built-in special functionsrelated to lists. In addition to difficulties closely related to lists, some difficulties related to previously learned material such as loops and branching were noticed, which can serve as a good incentive for conducting future research. The results of this research can be used as a guideline for current and future computer science teachers in improving and advancing the teaching in their classrooms.