Common variable immunodeficiency (CVID) is primary hypogammaglobulinaemia with an unknown aetiopathogenesis. Although various abnormalities of T and B cells have been described, their pathogenetic roles are unclear. We determined T and B lymphocyte subsets known to be abnormal in CVID in order to disclose possible relations between numerical abnormalities in those cells. Markers associated with B cell development (CD21, CD27, IgM, IgD) were determined on B lymphocytes (CD19⁺); T lymphocyte development (CD45RA, CD45RO, CD62L) and activation markers (CD25, CD27, CD28, CD29, CD38, CD57, HLA-DR) were determined on CD4⁺ and CD8⁺ T lymphocytes in 42 CVID patients and in 33 healthy controls. Abnormalities in CD4⁺ T lymphocyte activation markers (increase in CD29, HLA-DR, CD45RO, decrease in CD27, CD62L, CD45RA) were observed particularly in patients with a decreased number of memory (CD27⁺) and mature (CD21⁺) B cells (group Ia according to the Freiburg group’s classification), while abnormalities observed in CD8⁺ cells (increase in CD27 and CD28 and decrease in HLA-DR, CD57 and CD38) did not depend upon grouping patients together according to B lymphocyte developmental subpopulations. We observed correlations between immature B cells (IgM⁺ CD21^–) and expression of CD27, CD62L, CD45RA, CD45RO and HLA-DR on CD4⁺ T cells in CVID patients but not in the control group. The expression of CD27 and CD45RA on CD4⁺ T lymphocytes, such as the percentage of IgD⁺ CD27^– and IgD⁺ CD27⁺ cells in B lymphocytes, showed age dependency to be more significant than in the control group. Our study demonstrates that T and B lymphocyte abnormalities in CVID are partially related to each other. Some of those abnormalities are not definite, but may evolve with age of the patient.