Recent advances in immunology, cytogenetics and molecular genetics has allowed for a better understanding of the origin and evolution of non Hodgkin lymphoma (NHL). Over the last decade a number of recurrent chromosome aberrations has been disclosed and some correlations with well defined histologic subsets of B-cell NHL has been established. Five important cytogenetic-histologic associations has been documented, well defined by combined cytologic, immunologic and genetic investigations: t(14;18) (q32;q21) and NHL of follicle centre cell origin, frequently with follicular histologic pattern; t(8;14) (q24;q32) and Burkitt's lymphoma, Burkitt-like lymphoma or the equivalent small non-cleaved cell category of the "working formulation system"; t(3;22) (q27;q11) and diffuse large cell lymphoma; t(11;14) (q13;q32) and mantle zone lymphoma; trisomy 12 and chronic lymphocytic leukemia and well-differentiated small lymphocytic lymphoma. Molecular genetic studies elucidated some mechanisms operating during the normal lymphocyte differentiation which may be held responsible for the illegitimate recombination between the immunoglobulin genes and some oncogenes normally located on other chromosome regions. It has thus been demonstrated that the early events leading to neoplastic transformation in B-cell neoplasias occur in immature lymphocyte precursors in the bone marrow during the assembly of the immunoglobulin heavy chain gene. According to some recent studies chromosome changes may have prognostic value in B-cell NHL and chronic lymphocytic leukemia and may be employed in clinical practice in the construction of proportional hazard models in several histologic subsets of NHL.