ObjectiveLow self-esteem has been suggested as a putative mechanism in the development and maintenance of psychosis. Uncertainty still exists about how unstable self-esteem relates to psychotic experiences. The present study examines the potential (temporal) associations between momentary self-esteem, fluctuations in self-esteem, and psychotic experiences in daily life. MethodsExperience sampling data were collected from 46 individuals presenting with an at-risk mental state (ARMS), 51 individuals with first-episode psychosis (FEP), and 53 controls, to investigate associations between (fluctuations in) self-esteem and psychotic experiences within and across FEP, ARMS, and controls, using linear mixed models. ResultsIn all three groups we found that lower momentary self-esteem was associated with a greater intensity of psychotic experiences (adj. βFEP = −0.15, 95% CI -0.20 to −0.10, p = 0.000; adj. βARMS = −0.20, 95% CI -0.26 to −0.15, p = 0.000; adj. βcontrols = −0.12, 95% CI -0.17 to −0.07, p = 0.000). Variability in momentary self-esteem was associated with a greater intensity of psychotic experiences only in ARMS (adj. βARMS = 0.08, 95% CI 0.04 to 0.11, p = 0.000) and controls (adj. βcontrols = 0.04, 95% CI 0.01 to 0.08, p = 0.023). For instability this association held only in controls (adj. βcontrols = 0.03, 95% CI 0.00 to 0.05, p = 0.020). Furthermore, findings may suggest a reciprocal temporal association between self-esteem and psychotic experiences. ConclusionsOur findings suggest that self-esteem may be an important mechanism targetable by ecological momentary interventions to reduce the intensity of psychotic experiences and potentially prevent illness progression at an early stage.