A case of right-sided diaphragmatic hernia following group B streptococcal pneumonia and sepsis is reported herein. The clinical course was characteristic. The position of the right hemidiaphragm was initially normal. After an antecedent group B streptococcal infection, an abnormal shadow indicating either pneumonia or a pleural effusion on the chest x-ray was recognized and an elevation of the bowel and liver into the right hemithorax gradually appeared. Repair of the hernia was indicated and the postoperative result was excellent. The relationship between a delayed-onset diaphragmatic hernia and a group B streptococcal infection is still unknown. Increased intrathoracic pressure caused by mechanical ventilation coupled with an abnormal lung compliance due to inflammation may have resulted in the delayed herniation. Among various methods for diagnosis applied, chest x-ray and ultrasonography were noninvasive and useful.