Cluster headache attacks occurring in periods lasting from seven days to one year, separated by pain-free periods lasting at least one month.
A. Attacks fulfilling criteria for 3.1 Cluster headache and occurring in bouts (cluster periods)
B. At least two cluster periods lasting from 7 days to 1 year (when untreated) and separated by pain-free remission periods of ≥1 month.
Cluster periods usually last between two weeks and three months.