CD1 activates T cells, but the functions and size of possible human T cell repertoires recognizing each of the CD1 antigen presenting molecules remain unknown. Using an experimental system that bypasses major histocompatibility complex (MHC) restriction and the requirement for defined antigens, we found that polyclonal T cells responded at higher rates to cells expressing CD1a compared to CD1b, CD1c or CD1d. Unlike invariant NKT cells, the CD1a-autoreactive repertoire contains diverse T cell receptors. Functionally, many CD1a-autoreactive T cells home to skin, where they produce interleukin 22 (IL-22) in response to CD1a on Langerhans cells. The strong and frequent responses among genetically diverse donors define CD1a-autoreactive cells as a normal part of the human T cell repertoire and CD1a as a target of T H22 cells.