The theatre building in the main town of Kefalonia, designed to the 1959 seismic code for lateral loads about 30% of those specified today and suffering from reinforcement corrosion, was apparently the first application of Part 3 of Eurocode 8 for seismic assessment and retrofitting. Nonlinear dynamic analyses have shown that it could not survive earthquakes with peak ground acceleration (PGA) of about 0.05g. The retrofitting faced several constraints: minimal disruption of operation, access to the foundation only at the perimeter, no change to the façade and minimal intervention to the other sides, by employing at the perimeter one-sided RC or FRP overlays and two new walls, connection of the two structurally independent and torsionally imbalanced units of the building into a single one and one-sided FRP jackets at selected interior elements. Less than seven years later the building was subjected to an earthquake with a PGA of 0.39g. Damage was serious only in nonstructural masonry at the penthouse. Nonlinear dynamic analyses of the retrofitted or the original building agree with the observed performance and show that, had the building not been retrofitted, it would have collapsed.