T helper (T_h) cell activation is required for the adaptive immune response. Formation of the immunological synapse (IS) between T_hcells and antigen-presenting cells is essential for T_hcell activation. IS formation induces the polarization and redistribution of many signaling molecules; however, very little is known about organelle redistribution during IS formation in T_hcells. We show that formation of the IS induced cytoskeleton-dependent mitochondrial redistribution to the immediate vicinity of the IS. Using total internal reflection microscopy, we found that upon stimulation, the distance between the IS and mitochondria was decreased to values <200 nm. Consequently, mitochondria close to the IS took up more Ca²⁺than the ones farther away from the IS. The redistribution of mitochondria to the IS was necessary to maintain Ca²⁺influx across the plasma membrane and Ca²⁺-dependent T_hcell activation. Our results suggest that mitochondria are part of the signaling complex at the IS and that their localization close to the IS is required for T_hcell activation.