This book constitutes the proceedings of the 5th International Symposium on Model-Based Safety and Assessment, IMBSA 2017, held in Trento, Italy, in September 2017. The 17 revised full papers presented were carefully reviewed and selected from 29 initial submissions. The papers are organized in topical sections on safety process; safety models and languages; fault detection and propagation; safety assessment in the automotive domain; and case studies.