OBJECTIVE: Religious delusions are prevalent symptoms in schizophrenia. It is unclear, however, whether religious delusions reflect illness- or culture-related factors. METHODS: Cross-cultural retrospective comparison of the prevalence of religious delusions in 132 patients treated for paranoid schizophrenia in East Berlin (former GDR) from 1980 to 1985, and 151 patients from Regensburg (FRG) who were treated as in-patients from 1980 to 1983. RESULTS: Prior to the German re-unification, religious delusions were significantly less frequent in East Berlin compared to Regensburg (11.6% as opposed to 28.6 %, chi2 = 8.029; p = 0.0046). CONCLUSIONS: The prevalence of religious delusions in schizophrenia is, above all, associated with cultural factors. Religious delusions are therefore secondary phenomena in schizophrenia, and not inherent to the illness process.