AIM: To evaluate the relationship between the incidence of primary post-tonsillectomy haemorrhage and the daily weather condition, over a five-year period. STUDY DESIGN and SETTING: This was a retrospective study carried out in the ENT department of the Split University Hospital between January 2000 and December 2004. RESULTS: Out of 3377 patients undergoing tonsillectomy, primary post-operative haemorrhage occurred in 83 (2.5 per cent). The season, daily atmospheric pressure and daily change in atmospheric pressure did not have any significant influence on post-tonsillectomy haemorrhage incidence. However, there was a statistically significant increase in the incidence of primary post-operative haemorrhage when cyclonic conditions prevailed (p Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 0.035). CONCLUSION: The incidence of primary post-tonsillectomy haemorrhage in our study population was 2.5 per cent. Avoiding tonsillectomy during cyclonic weather conditions may reduce the incidence of primary post-tonsillectomy haemorrhage.