Background: This study investigated the role of cognitive mechanisms underlying obsessive compulsive and panic disorders in psychosis, and in particular, their possible contributions to acute psychosis. Method: A total of 90 participants were recruited comprising three equal-size groups, including two clinical groups (acute and stable) and one non-clinical matched control group. Symptom severity and distress was assessed using the PSYRATS, and questionnaire measures of anxiety and obsessive beliefs were administered to all participants. Results: Individuals with a diagnosis of psychosis reported significantly higher levels of obsessional beliefs and anxiety sensitivity than the non-clinical group. Furthermore, acutely psychotic patients reported a significantly higher sense of responsibility and catastrophic misinterpretation than the stable psychiatric controls, and than samples of OCD and GAD patients. Conclusions: Results suggest that these anxiety processes are particularly important during acute psychotic episodes, beyond the reported comorbidity. The theoretical and clinical implications of these findings, the limitations of the methodology employed, and suggestions for future research are discussed.