Restriction fragment length polymorphism (RFLP) analysis carried out on 45 primary neuroblastomas showed deletion of chromosome 11 sequences in 12 of 37 (32%) informative cases. Both 11p and 11q probes were informative in seven tumors; loss of all of chromosome 11, of only 11p sequences, and of only 11q sequences was observed in 4, 1, and 2 tumors, respectively. A cytogenetic abnormality involving translocation of chromosome arm 11q to chromosome arm 1p was observed in a primary tumor. Deletion of 14q was observed in 6 of 27 (22%) informative cases. Deletion of chromosome 11 but not 14q may correlate with regional and metastatic disease. These results suggest a possible role for sequences localized to chromosome 11 and to 14q in the development and/or progression of neuroblastoma.