A case of pineoblastoma with an interesting cytogenetic abnormality is reported. Chromosomal analysis of cultured cells from the tumor of a 10-week-old white male revealed an interstitial deletion of the long arm of chromosome 11, del(11)(q13.1q13.5). Tumors of the pineal region are relatively rare, and this is the first report of a pineoblastoma with del(11q).