This study aims to examine the types of mathematical connections that pre-service mathematics teachers use in their instructions and their opinions on the mathematical connection. For this purpose, a total of 60 pre-service mathematics teachers made lesson plans related to a learning objective from the Turkish middle school mathematics curriculum. The case study design, which is one of the qualitative research methods, was adopted in the study. Video recordings, field notes and an opinion form were used as data collection tools. The data were analyzed using content analysis method. Results of the study show that almost all of the pre-service teachers have an understanding of mathematical connections. It was determined that the types of connections between concepts, between different representations and connections with real life were prominent, while the type of association with different disciplines was less common during the instructions. Connections were mainly made by giving examples through verbal expressions. These results provide an important perspective on the mathematical connection skills of pre-service primary mathematics teachers. Suggestions for improving pre-service teachers' mathematical association skills were presented according to the results of the study.