Background: In previous functional magnetic resonance imaging (fMRI) studies, participants with schizophrenia showed decreased language lateralisation, resulting from increased activation of the right hemisphere compared with controls, Aim: To determine whether decreased lateralisation and increased right cerebral language activation constitute genetic predispositions for schizophrenia. Method: Language activation was measured using fMRI in 12 right-handed monozygotic twin pairs discordant for schizophrenia and 12 healthy right-handed monozygotic twin pairs who were matched for gender, age and education. Results: Language lateralisation was decreased in discordant twin pairs compared with the healthy twin pairs. The groups did not differ in activation of the language-related areas of the left hemisphere, but language-related activation in the right hemisphere was significantly higher in the discordant twin pairs than in the healthy pairs. Within the discordanttwin pairs, language lateralisation was not significantly different between patients with schizophrenia and their co-twins. Conclusions: Decreased language lateralisation may constitute a genetic predisposition for schizophrenia.