CRTAM was reported as a novel receptor expressed in activated NKT and CD8 T lymphocytes. However, we have recently shown that it is also expressed in several non-immune tissues. In opposition to what has been stated for lymphoid cells, CRTAM expression is constitutive in epithelia, suggesting a role in cell-cell interactions. Given the importance of cell interactions during T lymphocyte development, we evaluated CRTAM during T lymphocyte ontogeny. Here we show that CRTAM has an unexpected constitutive expression in adult thymocytes and, remarkably, it is sustained during all stages of thymocyte development. CRTAM expression is restricted to CD8 and all DN subpopulations, with a consistent pattern from E13.5 stage to adult mice. Blocking CRTAM interaction with CADM1 impairs thymus growth, uncovering a novel role in thymus development, with a consequent impact in thymocyte maturation. Thus, CRTAM interaction with CADM1 is involved in structural maintenance of the thymic lobes.