Nonrandom aberrations of chromosome 7 have been described in various hematopoietic disorders. We describe here two unrelated families with the same constitutional inversion of chromosome 7 [inv(7)(q11.2q22)]. The probands in both families had acute leukemia and cytogenetic analysis revealed that the inversion was the sole cytogenetic abnormality in the bone marrow at diagnosis. There is a history of hematologic diseases in one of these families that included a son who is a carrier of this constitutional inversion. The distal inversion breakpoint lies within the common region of chromosome loss identified in some myeloid diseases. These observations raise the possibility that this inherited chromosome rearrangement could result in a mutation of a tumor suppressor gene and possibly represent a predisposing event for the development of leukemia in these individuals.