For the new main level in the Kiirunavaara mine, new ventilation shafts and ore passes had to be made. The method chosen for the excavation was raise boring. This thesis describes an analysis of the raise boring performed, and gives suggestions on how to optimize the raise boring. The analysis is made in two parts, a reliability analysis and an analysis of the drilling. The reliability analysis investigates the reliability measures, such as availability, degree of usage and mean time between failures. The analysis of drilling mainly concerns the achieved penetration rates, and the factors influencing the penetration rates. Some statistical analyses are also made on the penetration rates. Based on the analyses, suggestions for improvements in order to optimize the raise boring, and the use of the raise boring machines are given.