OBJECTIVES: The seasonal variation in many medical conditions is well established. Studies have also shown a seasonal variation of hospital admissions of some abdominal infections. Upper respiratory tract infections have a definite seasonal variation. However, there are hardly any studies regarding the seasonal variation of the generic or disease-specific health-related quality of life (hrQoL) in patients having sinonasal diseases. The aim of this study was to assess the seasonal variation of hrQoL in patients having different sinonasal diseases. METHODS: This was a cross-sectional, questionnaire-based study. All scheduled adult patients that were referred to the Helsinki University Central Hospital Department of Otorhinolaryngology because of a rhinologic disease or sinonasal symptoms within the study months were invited to participate. The study periods were four months: February, May, August and November in 2014. The patients were sent a generic hrQoL-questionnaire (15D) and a rhinologic disease-specific hrQoL-questionnaire (SNOT-22). Accurate weather reports were obtained from the Finnish Meteorological Institute. In 2014 the monthly mean temperatures in Helsinki-Kaisaniemi weather station in Feb, May, Aug and Nov were +0.2, 10.6, 17.9 and 3.2 °C. RESULTS: Our study consisted of 306 patients. The mean 15D scores in Feb (N=72), May (N=78), Aug (N=67) and Nov (N=89) months were 0.868, 0.861, 0.868 and 0.870, respectively. There were no statistically significant differences (p=0.948) between the mean monthly 15D scores. The mean total SNOT-22 values in the study months were 41.0, 36.9, 36.5 and 35.8, respectively. There were no statistically significant differences between the mean SNOT-22 seasonal values. CONCLUSIONS: Our study showed that there was no seasonal variation in generic 15D or disease-specific SNOT-22 hrQoL scores when used in a patient population having different rhinologic diseases. Thus the named hrQoL questionnaires can be used in the follow-up of rhinologic patients with no concern of the effect of the four seasons.