In this study we analyzed nonrandom aberrations affecting chromosome 9 in a series of 426 consecutively ascertained, karyotypically abnormal non-Hodgkin's lymphoma (NHL) tumors derived from 407 patients. Cytogenetic abnormalities were correlated with clinical, histologic, and immunologic features. Structural abnormalities of chromosome 9 were identified in 60 specimens derived from 59 patients. The recurring abnormalities among these were associated with 4 clinico-pathologic subsets. The first comprised 7 cases of t(9;14)(pl3;q32), 6 of which had small lymphocytic lymphoma, plasmacytoid subtype, and an indolent clinical course. The second group included I 2 cases with breaks at 9q I I -I 3 and diffuse lymphomas with a large-cell component and a typical response t o combination chemotherapy. The third group was comprised of 7 cases with 9q deletions, with a common deleted region encompassing 9q3 1-32. These cases were characterized by diffuse B-cell histology, young age, and poor clinical outcome. The fourth subset included 5 intermediateto high-grade T-cell tumors with breaks at 9q34. This analysis of chromosome 9 aberrations in NHL comprises the first such effort based on a large series of tumors. We identify and report here new clinico-pathologic subsets with shared abnormalities of chromosome 9, which should facilitate new approaches t o the analysis of the etiology and clinical behavior of NHL. Genes Chrom Cancer 7:1-7 (1993).