Abstract Objectives Dwelling about positive experiences has been found to be positively related to mania and grandiose ideas. Nevertheless, besides some important limitations, past research has also neglected the nature (or characteristics) of memories individuals dwell on, and that might be specifically associated with grandiose ideas. Thus, the present study aimed to replicate previous studies while considering the role of specificity and the importance of memory used to increase grandiose feelings. Method In total, 219 participants were included and, after completing the memory induction, were randomized to either the rumination condition or the distraction condition. They also completed different questionnaires assessing positive rumination and grandiose ideas. Results Overall, rumination, compared to the distraction condition, led to the maintenance of grandiose ideas and positive affect from T2 to T3. Regression analysis showed that the specificity of memory was associated with grandiose ideas at T2, which predicted grandiose ideas at T3. Conclusions Our results confirm rumination's causal role in forming grandiose ideas. We also found that autobiographical memory and, more specifically, the capacity to recall past positive experiences coupled with repeatedly thinking about them might constitute a fundamental pathway leading to the persistence of such beliefs. The use of a non‐clinical sample limits the results and needs replication in clinical samples.