The adapter protein CrkL has been implicated in multiple signal transduction pathways in hematopoietic cells. In T lymphocytes, the recruitment of CrkL‐C3G complexes has been correlated with hyporesponsiveness, implicating CrkL as a potential negative regulator. To test this hypothesis we examined T cell activation in CrkL‐deficient mice. The CrkL^–/– genotype was partially embryonic lethal. In viable CrkL^–/– mice, peripheral blood counts were normal. The thymus from CrkL^–/– mice had 40% fewer cells compared to littermates, but the proportion of thymocyte subsets was comparable. There was no discernable alteration in T cell function as reflected by T cell numbers, expression of memory markers, IL‐2 production, proliferation, and differentiation into Th1/Th2 phenotypes. Immunization induced comparable levels of IgG2a and IgG1 antibodies. Chimeric mice, generated by transfer of CrkL^–/– fetal liver cells into irradiated RAG2^–/– recipients, also showed normal T cell function, arguing against selection via partial embryonic lethality. Our results indicate that CrkL is not absolutely required for T cell development or function, and argue against it being an essential component of a negative regulatory pathway in TCR signaling.