The Diagnostic and Statistical Manual of Mental Disorders (DSM) descriptive criterial approach to diagnosis has been criticized for contributing to comorbidity, heterogeneity within conditions, and nonspecificity across conditions. Much research has examined comorbidity and heterogeneity, but less is known about nonspecificity. Here, we examined two nonspecific symptoms: irritability and sleep disturbance. Both are common, clinically significant, and appear in several DSM disorder criteria sets, but their transdiagnostic prevalence is unknown. Leveraging a nationally representative epidemiological study of adolescents (n = 10,148; ages = 13-18), we first identified all instances where irritability or sleep disturbance appears in DSM-5-TR criteria for bipolar, depressive, anxiety, traumatic stress, or disruptive/impulse-control disorders; then found their DSM-IV equivalents in study variables; and finally estimated their prevalence individually and cumulatively across categories. Weighted lifetime prevalence estimates were 79.5% (95% CI [77.8, 81.2]) for irritability and 60.8% [58.7, 62.9] for sleep disturbance. Associations with age and gender were significant but small. Most youth reported multiple symptoms of irritability (weighted M = 3.04, Mdn = 2) and at least one symptom of sleep disturbance (weighted M = 1.61, Mdn = 1). Both problems were extremely common among individuals with specific disorders but were underestimated by the criteria for those conditions. Results suggest that the high prevalence of DSM-defined irritability and sleep problems may be obfuscated by these symptoms being scattered across diagnostic entities. There is a need for more research on assessing, treating, and understanding problems related to irritability and sleep in their own right, cutting across, rather than confined to, particular diagnoses. (PsycInfo Database Record (c) 2023 APA, all rights reserved).