Specific chromosomal abnormalities such as chromosome 13 deletions and some translocations affecting the immunoglobulin heavy chain (IGH) gene, namely t(4;14)(p16;q32) and t(14;16)(q32;q23) have been associated with an adverse prognosis in multiple myeloma. Conventional cytogenetic techniques fail to detect these aberrations in the majority of cases. Thus, we have developed a novel set of interphase fluorescence in situ hybridization (I-FISH) assays targeting those regions frequently lost on chromosome 13 as well as those oncogenes most recurrently involved in translocations with the IGH locus in multiple myeloma, i.e. IRTA1/2 (1q21), FGFR3/MMSET (4p16), CCND3 (6p21), IRF4 (6p25), CCND1 (11q13), MAF (16q23), and MAFB (20q12). The probes were combined in a multicolor fashion to develop novel multicolor I-FISH (MI-FISH) assays, whose validity and applicability was evaluated in negative controls and in a series of 13 plasma cell neoplasias. Additionally, a combination of the novel MI-FISH assays with staining for the plasma cell-specific antigen VS38c by means of multicolor FICTION (M-FICTION, fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms) allowed us to selectively analyze the plasma cell compartment, and thereby to increase the assay sensitivity.