Monosomy 17 and structural abnormalities of the short arm of chromosome 17 have been reported to influence prognosis and treatment outcome in patients with non-Hodgkin's lymphoma (NHL). In diffuse large cell lymphoma, these abnormalities were associated with refractoriness to chemotherapy, higher proliferative rate and poor prognosis. We studied the incidence of chromosome 17 abnormalities in 55 patients with NHL by using fluorescence in situ hybridization with a directly conjugated centromeric probe for chromosome 17. Twenty-three patients (42%) were previously untreated. Thirty-four patients (62%) had diffuse large cell lymphoma, 18 (33%) had follicular low-grade lymphoma, one had small lymphocytic lymphoma, one had diffuse mixed cell lymphoma, and one had mantle cell lymphoma. Cells from benign lymphoid hyperplasia were used as controls. Eight patients (15%) had trisomy 17 in 1.2-40.7% of cells and one patient (1.8%) had monosomy 17 in 68.8% of cells. We conclude that monosomy 17 is not common in NHL. Chromosome 17 deletions should be investigated with region-specific probes to determine their clinical relevance in NHL.