OBJECTIVE: To analyze the impact of the lunar cycle and season on the incidence 
of aneurysmal subarachnoid hemorrhage (SAH).
PATIENTS AND METHODS: The medical records of 111 patients who were admitted over 
a 5-year period to our department because of aneurysmal SAH were retrospectively 
reviewed. The date of aneurysm rupture was matched with the corresponding season 
and moon phase.
RESULTS: An incidence peak for aneurysm rupture (28 patients) was seen during 
the phase of new moon, which was statistically significant (p < 0.001). In 
contrast, no seasonal variation in the incidence of SAH was observed.
CONCLUSION: The lunar cycle seems to affect the incidence of intracranial 
aneurysm rupture, with the new moon being associated with an increased risk of 
aneurysmal SAH.