Cytogenetic analysis was performed in 47 newly diagnosed patients with agnogenic myeloid metaplasia (AMM); 32 had a normal karyotype (68%, group I), whereas 15 had clonal abnormalities (32%, group II). The most frequent abnormal findings were a 20q- deletion in six cases (either alone or within complex anomalies), interstitial 13q- deletion in three cases (and monosomy 13 in one case), and acquired trisomy 21 or 21p+ in three cases. Four cases exhibited complex aberrations involving several chromosomes, sometimes with a mosaicism. In two patients with an initial abnormal karyotype, further cytogenetic analysis during the disease course showed the appearance of additional clonal anomalies, and particularly of a probable Philadelphia (Ph1) variant in one case. Treatment was essentially supportive. Survival was significantly shorter in group II (median, 30 months) compared with group I (median, not reached at 6 years; P = .015). In univariate analysis, other parameters significantly associated with a poor prognosis (P less than .05) were higher age, anemia, and increased percentage of circulating blasts. However, in a multivariate analysis, only cytogenetic abnormalities and age retained their independent prognostic value.