Decades of research has examined the difficulty that people with psychiatric diagnoses have in recalling specific autobiographical memories of events that lasted less than a day. Instead, they seem to retrieve general events that have occurred many times or which occurred over longer periods of time, termed overgeneral memory. We present the first transdiagnostic meta-analysis of memory specificity/overgenerality and the first meta-regression of proposed causal mechanisms. A keyword search of Embase, PsycARTICLES, and PsycINFO databases yielded 74 studies that compared people with and without psychiatric diagnoses on the retrieval of specific (k = 85) or general memories (k = 56). The majority of studies included participants with Major Depressive Disorder (∼49%), Schizophrenia (∼19%), and Posttraumatic Stress Disorder (∼17%) with few studies involving other groups of participants, for example, Anxiety Disorders (∼5%). Multilevel meta-analysis confirmed that people with psychiatric diagnoses typically recall fewer specific, g = -0.864, 95% CI [-1.030, -0.698], and more general, g = 712, 95% CI [0.524, 0.900], memories than diagnoses-free people. The size of these effects did not differ between diagnostic groups. There were no consistent moderators of effect size heterogeneity; effect sizes were not explained by methodological factors such as cue valence or demographic variables such as participants' age or between-group differences in process variables (e.g., rumination). Deficits in autobiographical memory retrieval may be a transdiagnostic factor, but further research in underrepresented diagnostic groups, and with novel experimental manipulations of encoding and retrieval processes, is warranted before full transdiagnosticity and the processes underlying reduced specificity/overgenerality can be established. (PsycInfo Database Record (c) 2022 APA, all rights reserved).