Case studies published over 40 years ago suggest that seriously mentally ill patients appear to report more severe psychotic symptoms when assessed in their mother tongue as opposed to a later acquired language. We aimed to test this hypothesis empirically in both a clinical sample of 222 patients with schizophrenia/schizoaffective disorder (Study 1) and a nonclinical sample of 414 undergraduates (Study 2), focusing on positive and disorganized symptoms (clinical and subclinical, respectively), which have been indicated as most influenced by sociocultural factors. In Study 1, participants interviewed in their mother tongue endorsed significantly greater symptom severity than those interviewed in a later-acquired language on the Thought Disturbance subscale of the Brief Psychiatric Rating Scale, but no differences on the Disorganization subscale. In Study 2, participants who were assessed in their mother tongue reported significantly greater Unusual Experiences and Cognitive Disorganization on the Oxford-Liverpool Inventory of Feelings and Experiences than those responding in an acquired language. Results supported the hypothesis that evaluations conducted in an individual’s mother tongue reveal greater psychopathology than those conducted in a later acquired language. Clinical implications regarding language use in assessment are discussed.