- Assessment of existing structures should be based on the actual as-built conditions concerning geometry, material properties, loading and environmental conditions. A crucial step of the assessment consists in updating of prior information by newly obtained measurements which may be conducted by Bayesian approach. Updating of probabilistic distributions of basic variables or direct updating of failure probability can be effectively used. Application of theoretical principles is illustrated by a case study of a historic factory built in 1900s. The paper is a tribute to Ton Vrouwenvelder for his essential contributions to developments of theory and promotion of practical applications of probabilistic assessment of existing structures.