The experience from in-service inspection of the offshore concrete platforms installed in the North Sea up to 1989 are summarized. The concrete structures have performed remarkably well in the hostile North Sea environment. No significant signs of material deterioration, corrosion of reinforcement or other material related deficiencies have been observed. In the submerged zone the reinforcement appears well protected against corrosion by the cathodic protection. Observed deficiencies are mainly caused by falling objects or ramming ships. The good performance is attributed mainly to good concrete quality, i.e., the low permeability of the concrete in situ.