Background: Functional somatic symptoms (FSS), that is, symptoms that cannot be conclusively explained by organic pathology, have a poorly understood aetiology. Intelligence was studied as a risk factor for FSS. It was hypothesised that intelligence is negatively associated with the number of FSS. To investigate the specific role of intelligence in FSS as opposed to medically explained symptoms (MES), the association of intelligence with FSS was compared with that of intelligence with MES. It was also hypothesised that lifestyle factors and socioeconomic factors mediate the relationship between intelligence and both FSS and MES, whereas psychological distress is especially important for FSS. Methods: All analyses were performed in a longitudinal study with two measurement waves in a general population cohort of 947 participants (age 33-79 years, 47.9% male). The Generalized Aptitude-Test Battery was used to derive an index for general intelligence, and the somatisation section of the Composite International Diagnostic Interview was used to measure the number of FSS and MES. Results: General intelligence was significantly associated with the number of FSS. The association of intelligence and FSS but not MES was mediated by work situation: participants of lower intelligence who reported more FSS were more often (unwanted) economically inactive. No evidence was found for a mediating role of psychological distress in the association of intelligence with FSS, even though distress was an important predictor of FSS. Conclusion: Intelligence is negatively associated with the number of FSS in the general population. Part of the association of intelligence with FSS is explained by a more unfavourable work situation for adults of lower intelligence.