Rationale:We describe 1 case of fetal giant pericardial cyst was diagnosed by fetal echocardiography in the second trimester, and the changes of the cyst were recorded by follow-up observation in the late trimester and after birth. We then review and discuss the knowledge about its diagnosis and treatment.Patient concerns:A 34-year-old pregnant woman was referred to our hospital because of a diagnosis of a fetal pericardial effusion at 22 5/7 weeks at another hospital.Diagnosis:Fetal echocardiography revealed an irregular anechoic area in the right side of the fetal right atrium and right ventricle that was closely related to but not communicated with the pericardiumis and suggested fetal pericardial cyst. Fetal cardiothoracic magnetic resonance imaging showed cystic FIESTA signal in the right lung region, with clear boundary, and a seemingly line-like low signal shadow within.Interventions:Since fetal pericardial cysts keep decreasing in size during maternal pregnancy, follow-up observation measures are taken.Outcomes:Fetal pericardial cysts disappear on their own 4 months after delivery.Lessons:Asymptomatic pericardial cysts in the fetal period can be followed up and observed, and intervention is performed only when the cyst rapidly enlarges or ruptures and becomes infected in the fetal or neonatal period. Echocardiography can be used as a first-line detection method for their initial detection and follow-up.