Anti-angiogenesis therapy with thalidomide has been reported to have marked activity in multiple myeloma (MM). As cytogenetics is an independent prognostic factor in MM, we analysed bone marrow (BM) angiogenesis and cytogenetic abnormalities in 34 patients with active MM. BM microvessel density (MVD), as determined by staining with anti-CD34, was significantly higher in MM (MVD: 221 +/- 94 per mm2) than in controls (80 +/- 36; P < 0.0001). In patients with the presence of at least one unfavourable cytogenetic abnormality (deletion of 13q14, deletion of 17p13, aberrations of 11q), a significantly increased BM MVD was observed (254 +/- 93 vs. 160 +/- 60 in patients with absence of these abnormalities; P = 0.0035). Further analyses indicated that increased BM MVD was significantly correlated with deletion of 13q14 (259 +/- 96 vs. 188 +/- 80; P = 0. 026), but not with other cytogenetic, clinical and laboratory MM parameters. We conclude that BM neovascularization is particularly high in MM with deletion of 13q14, which provides a rationale for use of anti-angiogenic strategies in the treatment of MM with high-risk cytogenetics.