Ventral brainstem compression is common in patients with basilar invagination associated with type I Chiari malformation. The aim of this study was to investigate the reliability of a combined one-session anterior-posterior surgical approach for these patients. Nine patients underwent transoral odontoidectomy, posterior foramen magnum decompression, occipitocervical fixation, and bone grafting. All but two patients had ventral and dorsal operations in one surgical sitting. One of these two individuals had previously undergone posterior decompressive surgery at another hospital, but his condition had deteriorated rapidly afterward. The mean follow-up time was 19 months (range, 14-30 months). There was no mortality and no significant morbidity in this series. All but one of the patients showed significant improvement in their symptoms. Chiari malformations have a surprisingly high association with basilar invagination, and patients may have symptoms in both conditions. If there is a marked anterior compression, anterior transoral and posterior decompression, fusion, and instrumentation is an optimal strategy for treating patients with basilar invagination associated with type I Chiari malformation.