© 2002 Coastal Education and Research Foundation, Inc.In the reliability-based risk assessment, the second order reliability index (βII) method and the Conditional Expectation Monte Carlo (CEMC) simulation were utilised in order to analyse the safety levels of Haydarpasa Port main breakwater, Sea of Marmara, Turkey. The failure probability was forecasted in the βII method by approximating the Hudson performance surface with a second-degree polynomial having an equal curvature at the design point where the design and structural parameters were taken into consideration. In the past, applications of reliability-based risk assessment methodology in Turkey for design conditions, only wave characteristics, tidal range, storm surge, wave set-up and the structural system parameters were included. Tsunami risk was not considered a major design parameter and was not included in the computations. In this study, a structural stability criterion in coastal engineering is suggested to achieve a common definition of reliability including the tsunami risk. The model introduced in this study is a practical technique for reliability-based risk assessment of breakwaters subject to tsunami risk. In order to determine the occurrence probability under design conditions, which is a function of storm waves, tidal range, storm surge and tsunami height, the CEMC simulation was interrelated with the βII method. From the reliability-based risk assessment model applied to Haydarpasa port as a pilot study in Turkey it was found that, inclusion of the tsunami risk increases the failure risk of the structure, and as lifetime of the structure increases, the impact of tsunami risk on the failure mechanism is more important. For Haydarpasa port main breakwater, tsunami was not the key design parameter when compared to storm wave, however, in places with great seismic activity, tsunami risk may be very significant depending on the occurrence probability and the magnitude of the tsunami.