OBJECTIVE : To determine whether there is a relationship between the age of seizure onset and the age of menarche. METHODS : 1144 women with epilepsy (WWE) in the community, ages 18-47 years, provided web-based survey data. We compared the frequencies of the individual differences between their ages of seizure onset and menarche to each other and chance. We determined whether the age of menarche is a predictor of the age of seizure onset and the percentage of the variance that menarche explains. We used two-step cluster analysis to auto-identify a cluster of years relative to the age of menarche that showed the greatest predilection for seizure onset. RESULTS : Average age of menarche was 12.55 [95% CI: 12.45-12.65]. It was greater in WWE who developed seizures before versus after menarche (12.70 [12.54-12.86] v 12.42 [12.30-12.54], p = 0.006). More WWE had seizure onset during the year of menarche than during any other year (8.3% v expected 2.1%; p < 0.0001). Menarche, however, explained only 1% of the variance. Seizure onset frequencies were greatest for an auto-identified cluster that spanned 2 years before to 6 years after menarche and subsumed 49.3% of seizure onset. CONCLUSIONS : Although the results indicate a significant relationship between the age of seizure onset and the age of menarche, the broader auto-identified perimenarchal cluster that subsumes 49.3% of seizure onset suggests that research target the potential role of the great increase in adrenarchal, as well as gonadarchal, neuroactive steroids that modulate neuronal excitability and seizures during that span.