Thymic cyst is regarded as a rare anomaly, accounting for about 3% of all anterior mediastinal masses. It can be either congenital or acquired. Congenital thymic cysts are usually asymptomatic, with about 50% found incidentally in childhood or adolescence. We report a case of 1-month 23-day-old male baby who was antenatally diagnosed at 32 weeks' gestation. Spontaneous resolution did not take place in the antenatal or neonatal period; instead, there was an increase in size on follow-up imaging. The baby was successfully managed by surgical excision.