Globoid cell leukodystrophy (GLD) of Krabbe disease results from mutations in the galactocerebrosidase (GALC) gene. Previously, we had identified a large deletion in the GALC gene together with a C to T polymorphism at cDNA position 502 in a significant number of cases of infantile Krabbe disease; however, the deletion breakpoint had not been found. In this paper we show that the deletion is approximately 30 kb starting near the middle of the 12 kb intron 10, and includes all of the coding region through exon 17 plus an additional 9 kb. The deletion junction contains a 4 bp direct repeat and is preceded by sequence identified as belonging to the Alu family of interspersed repetitive elements. Using genomic DNA and a PCR-based test to detect normal and deleted sequences at that location, a large number of patients with all clinical types of GLD were analyzed. Of 21 infantile patients found to be heterozygous for the 502T polymorphism reported previously, 15 had the deletion, one could not tested and five, including a Hmong child, did not have the deletion. Sixteen other infantile patients previously tested were found to be either homozygous (10) or heterozygous (6) for the deletion. In addition, five patients with juvenile and adult GLD were found to be heterozygous for the deletion. In every case tested, the deletion was always found on the same allele as the 502T polymorphism. However, other disease-causing mutations have been found on the 502T allele. With careful genotype analysis these families can receive improved genetic information including patient and carrier identification and preimplantation diagnosis.