We report the isolation, genomic structure, chromosomal location, and expression pattern of the FEM1A gene, the human ortholog of the Caenorhabditis elegans fem-1 and mouse Fem1a genes. The coding sequence is 1851 bp and encodes a 617 amino acid protein. The human FEM1A protein has 65% identity with the mouse Fem1a protein and 34% identity with the C. elegans fem-1 protein, indicating conservation of this protein. The N-terminal region of the encoded protein contains six ankyrin repeat elements, a motif found in signaling and transcriptional regulatory molecules such as Notch and glp1. The gene was highly expressed in human kidney and cardiac tissue, and was expressed at lower levels in multiple tissues, including cartilage. FEM1A was localized to chromosome 5q23.1, a region of conserved synteny with a portion of mouse chromosome 17 that contains Fem1a. In C. elegans, fem-1 is involved in a pathway necessary for sex determination. The identification of a human homolog of this conserved gene suggests a potential role for this sex-determining molecule in humans.