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Traditional descriptions of delusions have emphasized the conviction with which they are held and their resistance to change. This study utilizes data from a large cohort of delusional subjects to assess the persistence and stability of delusional beliefs, and the predictors of change. Data were collected from 1,136 acutely hospitalized psychiatric patients, reinterviewed at 10-week intervals for 1 year. Persistence of delusional beliefs was determined for those delusional subjects with at least one follow-up visit (n = 405), and stability for the subset with delusions at two or more points in time (n = 262). Marked plasticity in delusional beliefs was observed, with one third of delusional subjects at any interview no longer delusional 10 weeks later. Persistence of delusions was associated with schizophrenia, global psychopathology, and having acted on a delusion, among other variables. Most subjects showed variation in the content of their primary delusion over time. Delusions appear to be more fluid over relatively short periods of time than has been suggested by many classic descriptions and contemporary formulations. DELUSIONS, the paradigmatic symptoms of psychosis, remain curiously underexplored, even as regards their essential characteristics. To what extent, for example, are delusions transitory phenomena that mark a particular stage of psychotic illness, as opposed to permanent stigmata that once present will always endure? The psychiatric literature appears to be of two minds about this question. Much theoretical writing sketches delusions as deeply held and resistant to change. Karl Jaspers’ influential characterization, for example, emphasized that delusions “are held with an extraordinary conviction, with an incomparable, subjective certainty,” and that “there is an imperviousness to other experiences and to compelling counter-argument” [emphasis in the original] (pp 95–96). 1 DSM-IV echoes that approach in defining a delusion as “A false belief … that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary” (p. 765). 2 Although depth of conviction at a given point does not preclude change over time, graphic accounts of the resistance of delusions to confrontation with reality 3 have reinforced the view of delusions as stable phenomena, as have arguments regarding the self-reinforcing aspects of delusional ideation. 4 On the other hand, considerable evidence exists of the plasticity of delusional beliefs. Delusions often fade or disappear with the resolution of an acute episode of psychosis, as most clinicians can testify from their own experience.5, 6 and 7 Longitudinal studies suggest that the presence of delusions may vary over time, and that in certain cases they may disappear entirely.7, 8, 9, 10, 11, 12, 13, 14, 15 and 16 For example, Jorgensen’s17 follow-up data on 75 patients with acute delusional psychoses, who were interviewed three times during the 8 years following discharge, showed that 43% were continuously delusional, 28% were intermittently delusional, and 29% had complete remissions. Recent data from Myin-Germeys et al.18 indicate that a group of schizophrenic subjects were delusional on average only 32% of the time. Even when delusions persist, some data indicate that the type of delusion that patients manifest and the delusional theme are susceptible to change.19 and 20 Given the evolving consensus about the plasticity of delusions,21 it is surprising that few efforts have been made to explore the predictors of this heterogeneity in the persistence and stability of delusional beliefs. In the study by Jorgensen mentioned above, a diagnosis of schizophrenia had by far the strongest predictive value for the persistence of delusions, followed by a primary delusion other than a delusion of reference, absence of psychosocial stressors prior to the index episode, and living alone.13 Harrow et al.15 also reported that delusions were significantly more likely to persist in schizophrenia than in schizoaffective or affective disorders. Duration of illness and presence of premorbid stressors were identified as predictors by Schanda et al.12 The importance of identifying those variables that are associated with persistence or remission of delusions is several-fold. Clinicians will be better able to predict the likely course of patients’ symptoms and perhaps better situated to intervene so as to mitigate their effects. Difficult diagnostic determinations may be aided by knowledge of patterns of delusional persistence characteristic of different disorders. In addition, the analyses may shed light on critical aspects of the psychopathological construct of delusions itself. If delusions are heterogeneous in their origins across differing diagnostic categories or delusional types (e.g., persecutory, grandiose, etc.), we may expect to see different patterns and predictors of remission in various diagnostic and typological groups. Alternatively, similar patterns of presentation over time despite diagnostic and other differences would be compatible with the view of delusions as unitary phenomena, as has previously been demonstrated for their non-content-related dimensional characteristics.22 Here, we explore the persistence and stability of delusional beliefs in a large and diverse sample of acutely hospitalized psychiatric patients, followed intensively for 1 year after discharge. In addition to examining the effect of diagnostic categories, we focus on type of delusion and non-content-related descriptors to assess their impact on patterns of delusional presentation.