Background: The vast majority of patient safety research has focused on somatic health care. Although specific adverse events (AEs) within psychiatric healthcare have been explored, the overall level and nature of AEs is sparsely investigated. Methods: Cohort study using a retrospective record review based on a two-step trigger tool methodology in the charts of randomly selected patients 18 years or older admitted to the psychiatric acute care departments in all Swedish regions from January 1 to June 30, 2017. Hospital care together with corresponding outpatient care were reviewed as a continuum, over a maximum of 3 months. The AEs were categorised according to type, severity and preventability. Results: In total, the medical records of 2552 patients were reviewed. Among the patients, 50.4% were women and 49.6% were men. The median (range) age was 44 (18-97) years for women and 44.5 (18-93) years for men. In 438 of the reviewed records, 720 AEs were identified, corresponding to the AEs identified in 17.2% [95% confidence interval, 15.7-18.6] of the records. The majority of AEs resulted in less or moderate harm, and 46.2% were considered preventable. Prolonged disease progression and deliberate self-harm were the most common types of AEs. AEs were significantly more common in women (21.5%) than in men (12.7%) but showed no difference between age groups. Severe or catastrophic harm was found in 2.3% of the records, and the majority affected were women (61%). Triggers pointing at deficient quality of care were found in 78% of the records, with the absence of a treatment plan being the most common. Conclusions: AEs are common in psychiatric care. Aside from further patient safety work, systematic interventions are also warranted to improve the quality of psychiatric care.