Background: We aimed to systematically review meta-analyses on the link between attention-deficit/ hyperactivity disorder (ADHD) and a broad range of psychiatric, physical, and behavioral health conditions (PROSPERO; no.CRD42023448907). Results: We identified 22 meta-analyses that included 544 primary studies, covering 76 unique conditions in over 234 million participants across 36 countries and six continents. We found high-certainty evidence for the associations between ADHD and neuropsychiatric conditions (bipolar disorders, personality disorders, schizophrenia, and pragmatic language skills), night awakenings, obesity, decayed incipient surfaces, asthma, astigmatism, hyperopia and hypermetropia, strabismus, and suicide ideation. Moderate-certainty evidence suggested that ADHD was associated with headache, mood/affective disorders, depression, bruxism, bone fractures, atopic rhinitis, vision problems, suicide attempts, completed suicide, and all-cause mortality. Lowcertainty evidence indicated associations with eating disorders, sleep efficiency, type 2 diabetes, dental trauma prevalence, atopic diseases, and atopic dermatitis. Very low-certainty evidence showed associations between ADHD and several sleep parameters. Conclusion: We found varied levels of evidence for the associations of ADHD with multiple health conditions. Therefore, clinicians should consider a wide range of neurological, psychiatric, sleep and suicide-related, metabolic, musculoskeletal, oral, allergic, and visual conditions, as well as the increased risk of mortality when assessing individuals with ADHD.