Sarcoidosis is a chronic disease with an unknown aetiology. Our aim was to evaluate the pattern of seasonality of stage 1 sarcoidosis subjects who had symptoms by all cases, by age and by both genders. In this study, we used Roger's test for cyclic variation to prove that this seasonal variation was more than chance.

Four hundred ninety-two consecutive patients with sarcoidosis who presented different clinical symptoms were included in this retrospective cohort study. According to the chest X-ray examinations, 185 patients had stage 1, while 307 patients in control group had stage 0, 2, 3 and 4 sarcoidosis.

The demographic features, presenting clinical features, course of the disease, initial diagnostic methods and both the month and the age at the initial diagnosis for each patient were analysed on chart reviews. Roger's test for cyclic variation was used to determine the significance of any seasonal variation of incidence. Otherwise, t-test was used.

The distribution of cumulative monthly presentations for patients with stage 1 peaked in April (108% above the average) and was lowest in October, November and December (48% below the average) (p < 0.001). Seasonality of the control group peaked in May (84% above the average) and was lowest in August (69% below the average) (p < 0.001). The seasonal pattern of subjects within both groups was influenced by some age groups and by both genders (p < 0.05).

Some differences in the amplitude of the seasonal variation by age and by both genders increase the possibility of interactions among age, gender and the disease. Further well-designed and prospective studies are required to better understand the importance of our findings and the pathogenesis of the disease.