Nonabsorbable silk sutures have been a frequently used foreign material in neurosurgery. In general, they are reliable and safe with minimal bio-incompatibility. Three pediatric neurosurgical patients came to clinical attention, however, because of delayed foreign-body reactions to silk sutures. The delayed atypical presentation of these patients delayed appropriate diagnosis and therapy. In two patients, the reaction presented as a delayed inflammation 7 years following surgical suture placement. In the other patient, the reaction caused delayed recurrent shunt failures and surgical wound breakdown. These three cases are used to introduce a discussion of the delayed response of the host to foreign material and its pertinence to neurosurgery. © 1987 Springer-Verlag.