Osteomalacia is the name given to bone mineralization defects. Histologically, it is characterized by a marked excess of non-mineralized osteoid, predominantly lamellar and with little or no osteoblastic activity adjacent to its surface. Osteoid thickness increases as an expression of mineralization delay. As a result, more than 4 birefringent collagenous layers are observed in an osteoid bed. In contrast to osteitis fibrosa, osteomalacia is a form of low turnover, i.e. with minimal or no cellular activity at the bone surface. In these cases double TCN labeling is low, absent, or may appear as a broad single label at the bone-osteoid interface.

In children, the term applied is rickets, and the mineralization defect occurs at the epiphyseal growth plate, producing widening of long bones epiphyses, retarded growth and skeletal deformities.