SignificanceOsteolectin promotes the maintenance of bone mass in adult mice, but there has not been genetic evidence that Osteolectin is functionally important in humans. In the current study, we identified a function for Osteolectin in juvenile mice: the promotion of bone elongation by increasing growth plate chondrocyte proliferation, leading to increased body length. Second, we describe a human genetic variant that suggests Osteolectin also promotes bone elongation in humans. The single-nucleotide variant (rs182722517) that is associated with reduced height and plasma Osteolectin levels in humans is also associated with reduced Osteolectin expression in bone marrow stromal cells.