Few empirical studies have examined the mental health of workers on North Sea oil and gas installations, and it is unclear from the available literature whether offshore employees show impaired mental health relative to their onshore counterparts. The present study was intended to clarify this issue by direct comparison of the General Health Questionnaire (GHQ) scores of onshore and offshore personnel engaged in similar work. As compared with published data, only the onshore group showed low GHQ-12 scores, although both groups were low in neuroticism. Analysis of GHQ subscale scores demonstrated that anxiety was significantly higher among offshore workers than among those working onshore, but there were no significant differences in somatic symptoms or social dysfunction. Regression analyses showed that this result was not affected by control for age, job level, and neuroticism, although there was a significant interaction between job level and neuroticism in predicting anxiety. The nature of the offshore environment, and the factors which may play a causal role in elevated anxiety among offshore workers, are discussed.