Survival of 5q(-)patients is known to depend on patient age, diagnosis, and acquisition of additional chromosome aberrations. The possible importance of the deleted 5q bands is unknown; nor is it known if the same or different factors are of prognostic importance in 5q(-)MDS and 5q(-)AML. In order to obtain material of sufficient size to answer these and other questions the literature was searched for 5q(-)cases with data on survival. Only MDS and AML cases with interstitial deletions were included. The results confirmed the prognostic importance of the factors mentioned above, but produced the following new data: In MDS, but not in AML, loss of the band 5q12 is an independent adverse prognostic factor; female patients survive longer in MDS while in AML men are the longer survivors; del(5)(q13q31) was found to be associated with MDS, 5q(-)as the sole aberration, and a long survival; on the other hand many del(5)(q12q32) cases showed AML, presence of additional aberrations, and short survivals. On the basis of these results the following hypotheses are proposed: 1) the female preponderance in 5q(-)MDS is due to longer female survival, and not to increased female incidence, and 2) some 5q deletions have a high diagnostic specificity, affect the rate of development of additional chromosome aberrations and thus in fact are major prognostic factors.