Adenomyosis is a clinical condition where endometrial glands are found in the myometrium of the uterus. One in three patients with adenomyosis is asymptomatic, but the rest may present with heavy menstrual bleeding, pelvic pain, or infertility. Heavy menstrual bleeding is the most common symptom. Adenomyosis is distinct from endometriosis (the presence of endometrial glands outside of the uterus), but the two conditions often occur simultaneously. Risk factors for developing adenomyosis include increasing age, parity, and history of uterine procedures. Most patients are diagnosed from 40 to 50 years of age, but younger patients with infertility are increasingly being diagnosed with adenomyosis as imaging modalities improve. Diagnosis of adenomyosis begins with clinical suspicion and is confirmed with transvaginal ultrasonography and pelvic magnetic resonance imaging. Treatment of adenomyosis typically starts with hormonal menstrual suppression. Levonorgestrel-releasing intrauterine systems have shown some effectiveness. Patients with adenomyosis may ultimately have a hysterectomy if symptoms are not controlled with medical therapy.