Two infants, an 11-month-old boy and a 7-month-old girl, presented with subarachnoidal abscess associated with severe bacterial meningitis refractory to intensive managements with antibiotics. Computed tomography (CT) revealed bifrontal extracerebral low-density areas and remarkably enhanced surfaces of the bilateral frontal lobes postcontrast. Surgical exploration disclosed thick pus accumulation in the subarachnoid space which required curettage. The boy developed appropriately for his age, but the girl showed severe psychomotor retardation because of additional complications such as subdural fluid collection and hydrocephalus associated with the subarachnoidal abscess. Appropriate early neurosurgical management of subarachnoidal abscess is essential for satisfactory psychomotor development. Postcontrast CT should be performed to detect the subarachnoidal abscess as early as possible, and extensive craniotomy to remove the subarachnoidal pus accumulation performed to preserve psychomotor development.