Objectives: Describe symptoms before and at time of register-diagnosis in children and adolescents. Methods: A random sample was selected for chart-review from a Danish nationwide cohort of patients <18 years registered with an incident ICD-10 register-diagnosis of single hypomanic/manic episode or bipolar disorder between 1995 and 2014. Patients with symptoms which adequately documented a BD diagnosis in the chart were included for analysis. Results: 521 were diagnosed in the study period. A random sample of 25% were selected, and 106 charts were possible to retrieve, with 48 chart reviews resulting in confirmation of diagnosis. Time from first reported affective symptoms to diagnosis was 2.6 ± 2.7 years for depressive symptoms, 2.5 ± 2.9 years for mixed symptoms, 1.4 ± 1.6 years for hypomanic symptoms, and 0.4 ± 0.5 years for manic symptoms. A hierarchical clustering analysis revealed three patient-profiles: primarily hypomanic/manic, primarily depressive, and more rare, primarily mixed profile. Frequently reported symptoms prior to diagnosis include anhedonia (79%), irritability (71%), hyperactivity (62.5%), decreased energy (62.5%), and psychotic symptoms (52%). Symptoms of ADHD (19%), comorbid ADHD (15%), symptoms of anxiety (52%), comorbid anxiety (4%), suicidal thoughts (50%), suicide attempts (8%), cutting (23%), substance misuse (21%), and criminal activity (10%) were reported before incident BD diagnosis. Conclusion: The observed patient-profiles leading to diagnosis were primarily manic or depressive, resembling presentations in adults. The presence of ADHD, anxiety, suicide attempts, cutting, and criminal activity prior to diagnosis emphasizes the need for treatment of children and adolescents with affective symptoms. The gap from appearance of the symptoms to diagnosis suggests a window for earlier treatment.