A propositus was presented manifesting the clinical picture of the D1 syndrome and demonstrating the chromosomal findings of a D/D translocation "trisomy." The increased level of Hb F usually seen in patients with this syndrome was serially demonstrated in the propositus over the first 9 months of life. In addition, the Hb A2 concentration was found to be significantly decreased during the same period. The hypothesis of maturational retardation was invoked to explain the hemoglobin changes and possibly the leucocytic changes in the usual D1 syndrome patient.