AbstractPurposeAlthough haemorrhage is a common and in some cases life-threatening complication after tonsillectomy, surprisingly little is known about the temporal fluctuations of the onset of bleeding. The purpose of this study was to assess circadian and seasonal rhythms of post-tonsillectomy haemorrhage (PTH) and potential ramifications to educate patients and health care staff.MethodsThis retrospective study carried out at a tertiary referral hospital included paediatric and adult patients requiring emergency surgery due to severe PTH between 1993 and 2019. Medical records were reviewed and patient demographics, details regarding the initial procedure, postoperative day of haemorrhage, and start time of emergency surgery were extracted. Descriptive statistics, Kruskal–Wallis test, Mann–WhitneyUtest, and Chi-square goodness of fit tests were used to detect potential differences.ResultsA total of 300 patients with severe PTH and subsequent emergency surgery were identified. The median postoperative duration until PTH was 6 (range: < 1–19) days. 64.7% (n = 194) of all emergency surgeries had to be performed during evening and night hours (6 pm—6 am) (p < 0.0001). Compared to diurnal incidents, the risk of a nocturnal PTH event increased, the longer ago the initial surgery was (p < 0.0001). No seasonal variations were identified. Age, sex, and details of the initial procedure had no significant influence on the start time according to the surgical protocol.ConclusionThe discovered temporal fluctuations of PTH are of relevance for patient awareness and preoperative education. Due to possible life-threatening complications, management of severe PTH requires specific resources and trained medical staff on call.