Paediatric acute-onset neuropsychiatric syndrome (PANS) is a newly defined symptom-based condition that mainly occurs in children and adolescents. Few studies have described the clinical characteristics of the syndrome. We clinically assessed and reviewed the medical histories of children and adolescents (aged 4-14 years) with suspected PANS who were referred to a specialist clinic in Gothenburg, Sweden, by local paediatricians and child psychiatrists. We scored severity of symptoms and impairment retrospectively for the timepoint with the most severe symptoms using the PANS scale. Of 41 patients (37 referred and four visited upon parents' request), 23 (ten girls and 13 boys) met PANS diagnostic criteria. Mean age at PANS onset was 8·5 years (SD 3·37). 11 (48%) patients had a family history of developmental or neuropsychiatric disorders in a first-degree relative and 11 (48%) had a family history of autoimmune or inflammatory diseases in a first-degree relative. 17 (74%) patients had been previously diagnosed with a developmental disorder (n=5) or had symptoms indicative of developmental problems (n=12). A verified or suspected infection was temporally related to PANS onset in all patients; the infection was bacterial in ten (43%) patients (eight had streptococcal infection and two an infection caused by other bacteria) and viral in 13 (57%) patients. All patients had a relapsing-remitting course of illness. The mean PANS scale symptom score was 46 (SD 3·67) and the mean impairment score was 45 (2·74). Antibiotic treatment was reported as beneficial by the parents of 12 (63%) of the 19 children who received antibiotics. Our PANS cohort had severe, acute-onset, complex neuropsychiatric symptoms, a relapsing-remitting symptom course, and possible infectious triggers. Further research into the cause of, and appropriate treatment for, PANS is warranted. Swedish Brain Foundation.