Introduction: Herpes simplex virus type 1 (HSV-1) reactivation can be induced by physical and chemical stress stimuli and/or with immunosuppression. Recurrent intraoral herpes (RIH) induced by a female sex steroid hormonal imbalance as a result of an adverse effect of oral contraceptive pills use is rare. Case report: A 40-year-old female patient presented with an 11-year history of recurrent oral ulceration. Drug history of oral contraceptive pills use for 16 years and of amenorrhea for the past 4 years were confirmed. Intraoral examination revealed multiple coalescing ulcers on the ventral tongue, palate, labial, and buccal mucosa. Serological test showed that anti-HSV-1-IgG was reactive. A female sex steroid hormone test showed low levels of estrogen and progesterone. Diagnosis of RIH induced by a hormonal imbalance due to oral contraceptive pills was made. Oral acyclovir-methylprednisolone combined therapy was given. RIH resolved in a 3-month follow-up. She had her periods back after stopping the pills and switching from oral contraceptive to intrauterine device (IUD). Discussion: RIH can be induced by a low level of female sex steroid hormone in an estrogen receptor-dependent manner. A low level of estrogen may inhibit cytotoxic responses of CD8+ T cell and by a leukocyte-independent effect on infected neurons resulting in susceptibility of oral mucosa to HSV-1 reactivation. The persistence of atypical lesions can be effectively managed by oral acyclovir-methylprednisolone combined therapy. Conclusion: Hormonal imbalance as one risk factor of RIH is important to be considered for preventing its recurrence. Oral acyclovir-methylprednisolone combined therapy and switching oral contraceptive pills to IUD showed a benefit in RIH treatment. Keywords: Hormonal imbalance, oral contraceptive pills, recurrent intraoral herpes