Cytogenetic and histopathologic data were correlated with clinical parameters from 423 patients with non-Hodgkin's lymphoma (NHL). Clinical correlations were performed on subgroups of 149 patients with low-grade lymphoma (LG) and 205 patients with diffuse lymphoma with a large cell component (DLLC). Correlations were made between clinical outcome and individual recurring cytogenetic aberrations, each of which was noted in greater than 5% of cases belonging to LG NHL and DLLC, and derived measures of karyotypic complexity, comprising modal chromosome number, number of marker chromosomes, and number of translocation breakpoints. No correlations with survival were noted in LG NHL, although median follow-up was only 2 years. Seven patients with t(8;14) LG NHL had an indolent course. Among 104 patients with DLLC and abnormal karyotypes at diagnosis, breaks at 1q21–23 or more than 4 marker chromosomes was associated with a shortened median survival. Using these variables we constructed a proportional hazards model with a good fit to observed data. Breaks at 6q21–25 predicted a decreased probability of achieving remission. Patients with DLLC and breaks at 1q21–23 or 1p32–36 had a shorter duration of complete remission. Of 41 DLLC studied at relapse, the only long-term survivors had t(14;18).