The aim of this study was to determine whether certain weather variables influence the secondary post-tonsillectomy haemorrhage rate and to examine the influence of a change in these variables on secondary haemorrhage. This was a prospective study carried out in a tertiary referral institution. All patients undergoing bilateral tonsillectomy over a one-year period were included. Local weather data, including daily temperature (max/min), relative humidity and water vapour pressure, were acquired. All patients readmitted to our department with secondary post-tonsillectomy haemorrhage were recorded. Of 346 patients undergoing tonsillectomy, 32 developed secondary haemorrhage (9.2 per cent). A significant negative correlation was found between secondary haemorrhage rate and the average monthly temperature (max/min) and water vapour pressure (Pearson’s correlation = −0.8) (p ≤ 0.002). These results suggest that performing tonsillectomy in warmer weather when the water vapour pressure is higher may reduce the secondary haemorrhage rate.