We asked in a retrospective analysis whether patients with diabetes mellitus or impaired glucose tolerance are at increased risk for morbidity and mortality after high-dose therapy followed by an autologous bone marrow transplantation. Nine patients with diabetes mellitus (n = 7) or impaired glucose tolerance (n = 2) were identified who had been treated with high-dose therapy and autologous bone marrow transplant for lymphoid malignancies. At the start of the pretransplant conditioning all patients had a Karnofsky score of at least 80 and no clinically demonstrable organ dysfunction. One patient with diabetes mellitus type I (DM I) was transplanted without any complications. The patients with diabetes mellitus type II (DM II) or an impaired glucose tolerance had complications of life-threatening infections (in 6/8), acute renal insufficiency (in 3/8), liver abnormalities with elevated liver enzymes or liver failure (in 4/8) and congestive heart failure (in 1/8). Although the complications observed are not infrequent in the transplant setting, because of the good performance status before BMT and the absence of clinically demonstrable organ impairment before transplantation, it is our impression that the presence of diabetes mellitus or glucose intolerance might be an important co-factor in the morbidity of these patients.