Three patients presenting with acute leukemic disorder and chromosome 3 rearrangement involving bands q21;q26 are reported, and the literature on chromosome 3q abnormalities is reviewed. All reported patients carrying a paracentric 3q inversion or a translocation 3;3 with breakpoints in q21;q26 had a myelodysplastic or acute leukemic disorder with a normal or elevated platelet count and lack of response to cytotoxic drug therapy. They showed an associated incidence of -7 or 7q- anomalies higher than de novo acute leukemia and appear to constitute a definite subgroup of the leukemic disorders with very poor prognosis. The majority of patients showing other chromosome 3 long arm rearrangements showed evidence of leukemic process, were in blastic crisis, or had been exposed to chemotherapy, exhibiting also a higher incidence of associated -5 or -7 cytogenetic abnormalities than is observed in patients not exposed to toxic agents.