Objective: To observe the therapeutic effect of Ommaya reservoir implantation on hydrocephalus in premature infants following intraventricular hemorrhage (IVH) and to investigate factors influencing the therapeutic effect. Methods: An ambispective cohort study was conducted on the clinical and follow-up data of 20 premature infants (gestational age <32 weeks, birth weight <1500 g) who received Ommaya reservoir implantation because of hydrocephalus following IVH. The therapeutic effect of Ommaya reservoir implantation was observed. These patients were divided into cure and treatment failure groups according to their treatment outcomes. The factors influencing therapeutic effects were investigated by univariate analysis. Results: Hydrocephalus was relieved significantly at 30 days after Ommaya reservoir implantation. However, some patients showed significantly decreased therapeutic effects since 3 months after operation: during 3-6 months after operation, 7 cases underwent ventriculoperitoneal shunt, 4 cases discontinued treatment because of economic reasons, and 1 case underwent endoscopic third ventriculostomy due to scalp hematoma with skin necrosis. The ventricles of the remaining 8 cases returned to normal size at 12-18 months after operation. As for postoperative complications, secondary IVH was seen in 8 cases, intracranial infection in 2 cases, and scalp hematoma with skin necrosis in 1 case. The univariate analysis revealed significant differences in gestational age, birth weight and duration of hydrocephalus before Ommaya reservoir implantation between the cure and the treatment failure groups (P < 0.05). Conclusions: Ommaya reservoir implantation has a remarkable short-term therapeutic effect on hydrocephalus in premature infants following IVH, but later the effect decreases in some patients. Low gestational age, low birth weight and long duration of hydrocephalus may be the main factors influencing therapeutic effects of Ommaya reservoir implantation.