A patient with mild choroideremia has been shown to carry a balanced translocation between chromosome X and 13-46,X,t(X;13)(q21.2;p12). Loci (DXY21, DX232, DX233) shown to map to this region on the X chromosome and in some cases to be deleted in other patients with choroideremia are intact in the DNA from this patient. To our knowledge this is the first report of a translocation associated with choroideremia. One of the translocation chromosomes, derivative 13, free of the derivative X and normal X, has been isolated in a somatic cell hybrid. Because of the clinical association of the eye findings with chromosome interchange, we suggest that the breakpoint on the X is at or near the choroideremia locus. Further analysis of this translocation may be useful in cloning the choroideremia gene.