Circannual rhythms and seasonality have long been in the interest of research. In humans, seasonal changes in mood have been extensively investigated since a substantial part of the population experiences worsening of mood during winter. Questions remain regarding accompanying physiological phenomena. We report seasonal effects on the acoustic startle response in a cross-sectional (n = 124) and a longitudinal sample (n = 23). Startle magnitudes were larger in winter (sample 1: p = 0.026; sample 2: p = 0.010) compared to summer months. Although the findings need to be replicated they may have implications regarding the timing of startle experiments.